Main Difference
The main difference between Circle and Sphere is that the Circle is a simple curve of Euclidean geometry and Sphere is a round geometrical and circular object in threedimensional space; special case of spheroid.

Circle
A circle is a simple closed shape. It is the set of all points in a plane that are at a given distance from a given point, the centre; equivalently it is the curve traced out by a point that moves so that its distance from a given point is constant. The distance between any of the points and the centre is called the radius. This article is about circles in Euclidean geometry, and, in particular, the Euclidean plane, except where otherwise noted.
A circle is a simple closed curve which divides the plane into two regions: an interior and an exterior. In everyday use, the term “circle” may be used interchangeably to refer to either the boundary of the figure, or to the whole figure including its interior; in strict technical usage, the circle is only the boundary and the whole figure is called a disc.
A circle may also be defined as a special kind of ellipse in which the two foci are coincident and the eccentricity is 0, or the twodimensional shape enclosing the most area per unit perimeter squared, using calculus of variations.

Sphere
A sphere (from Greek σφαῖρα — sphaira, “globe, ball”) is a perfectly round geometrical object in threedimensional space that is the surface of a completely round ball, (viz., analogous to a circular object in two dimensions).
Like a circle, which geometrically is an object in twodimensional space, a sphere is defined mathematically as the set of points that are all at the same distance r from a given point, but in threedimensional space. This distance r is the radius of the ball, and the given point is the center of the mathematical ball. These are also referred to as the radius and center of the sphere, respectively. The longest straight line through the ball, connecting two points of the sphere, passes through the center and its length is thus twice the radius; it is a diameter of the (sphere) ball.
While outside mathematics the terms “sphere” and “ball” are sometimes used interchangeably, in mathematics a distinction is made between the sphere (a twodimensional closed surface embedded in threedimensional Euclidean space) and the ball (a threedimensional shape that includes the sphere as well as everything inside the sphere). This distinction has not always been maintained and there are mathematical references, especially older ones, that talk about a sphere as a solid. This is analogous to the situation in the plane, where the terms “circle” and “disk” are confounded.

Circle (noun)
A twodimensional geometric figure, a line, consisting of the set of all those points in a plane that are equally distant from a given point (center).
“The set of all points (x, y) such that (x1)^{2} + y^{2}“
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“r^{2} is a circle of radius r around the point (1, 0).”

Circle (noun)
A twodimensional geometric figure, a disk, consisting of the set of all those points of a plane at a distance less than or equal to a fixed distance (radius) from a given point.

Circle (noun)
Any thin threedimensional equivalent of the geometric figures.
“Put on your duncecap and sit down on that circle.”

Circle (noun)
A curve that more or less forms part or all of a circle.
“move in a circle”

Circle (noun)
Orbit.

Circle (noun)
A specific group of persons; especially one who shares a common interest.
“inner circle;”
“circle of friends”

Circle (noun)
A line comprising two semicircles of 30 yards radius centred on the wickets joined by straight lines parallel to the pitch used to enforce field restrictions in a oneday match.

Circle (noun)
A ritual circle that is cast three times deosil and closes three times widdershins either in the air with a wand or literally with stones or other items used for worship.

Circle (noun)
A traffic circle or roundabout.

Circle (noun)
Compass; circuit; enclosure.

Circle (noun)
An instrument of observation, whose graduated limb consists of an entire circle. When fixed to a wall in an observatory, it is called a mural circle; when mounted with a telescope on an axis and in Y’s, in the plane of the meridian, a meridian or transit circle; when involving the principle of reflection, like the sextant, a reflecting circle; and when that of repeating an angle several times continuously along the graduated limb, a repeating circle.

Circle (noun)
A series ending where it begins, and repeating itself.

Circle (noun)
A form of argument in which two or more unproved statements are used to prove each other; inconclusive reasoning.

Circle (noun)
Indirect form of words; circumlocution.

Circle (noun)
A territorial division or district.
“The ten Circles of the Holy Roman Empire were those principalities or provinces which had seats in the German Diet.”

Circle (noun)
A bagginess of the skin below the eyes from lack of sleep.
“”After working all night, she had circles under her eyes.”

Circle (verb)
To travel around along a curved path.

Circle (verb)
To surround.

Circle (verb)
To place or mark a circle around.
“Circle the jobs that you are interested in applying for.”

Circle (verb)
To travel in circles.
“Vultures circled overhead.”

Sphere (noun)
A regular threedimensional object in which every crosssection is a circle; the figure described by the revolution of a circle about its diameter from 14th c..

Sphere (noun)
A spherical physical object; a globe or ball. from 14th c.

Sphere (noun)
The apparent outer limit of space; the edge of the heavens, imagined as a hollow globe within which celestial bodies appear to be embedded. from 14th c.

Sphere (noun)
Any of the concentric hollow transparent globes formerly believed to rotate around the heavenly bodies; there were originally believed to be eight, and later nine and ten; friction between them was thought to cause a harmonious sound (the music of the spheres). from 14th c.

Sphere (noun)
An area of activity for a planet; or by extension, an area of influence for a god, hero etc. from 14th c.

Sphere (noun)
The region in which something or someone is active; one’s province, domain. from 17th c.

Sphere (noun)
The set of all points in threedimensional Euclidean space (or ndimensional space, in topology) that are a fixed distance from a fixed point from 20th c..

Sphere (noun)
The extension of a general conception, or the totality of the individuals or species to which it may be applied.

Sphere (verb)
To place in a sphere, or among the spheres; to ensphere.

Sphere (verb)
To make round or spherical; to perfect.

Circle (noun)
a round plane figure whose boundary (the circumference) consists of points equidistant from a fixed point (the centre)
“draw a circle with a compass”

Circle (noun)
something in the shape of a circle
“the lamp spread a circle of light”
“they all sat round in a circle”

Circle (noun)
a dark circular mark below each eye caused by illness or tiredness
“she was pale and rather beautiful, with dark circles around deep, exhausted eyes”

Circle (noun)
a curved upper tier of seats in a theatre or cinema
“she sat in the front row of the circle”

Circle (noun)
short for striking circle

Circle (noun)
a group of people with a shared profession, interests, or acquaintances
“she did not normally move in such exalted circles”

Circle (verb)
move all the way around (someone or something), especially more than once
“they were circling Athens airport”
“we circled round the island”

Circle (verb)
move in a wide loop back towards one’s starting point
“he paced away from her, then circled back”

Circle (verb)
form a ring around
“the abbey was circled by a huge wall”

Circle (verb)
draw a line around
“circle the correct answers”

Sphere (noun)
a round solid figure, or its surface, with every point on its surface equidistant from its centre.

Sphere (noun)
a spherical object; a ball or globe
“the markers on the route included two conspicuous black spheres”

Sphere (noun)
a globe representing the earth
“the room was littered with books, maps, and spheres”

Sphere (noun)
a celestial body
“he sometimes took out his telescope to make sure the spheres were still revolving in good order”

Sphere (noun)
the sky perceived as a vault upon or in which celestial bodies are represented as lying.

Sphere (noun)
each of a series of revolving concentrically arranged spherical shells in which celestial bodies were formerly thought to be set in a fixed relationship.

Sphere (noun)
an area of activity, interest, or expertise; a section of society or an aspect of life distinguished and unified by a particular characteristic
“political reforms to match those in the economic sphere”

Sphere (verb)
enclose in or as if in a sphere
“mourners, sphered by their dark garb”

Sphere (verb)
form into a rounded or perfect whole
“you, hitherto, have still had goodness sphered within your eyes”