Main Difference
The main difference between Oval and Circle is that the Oval is a shape and Circle is a simple curve of Euclidean geometry.

Oval
An oval (from Latin ovum, “egg”) is a closed curve in a plane which “loosely” resembles the outline of an egg. The term is not very specific, but in some areas (projective geometry, technical drawing, etc.) it is given a more precise definition, which may include either one or two axes of symmetry. In common English, the term is used in a broader sense: any shape which reminds one of an egg. The threedimensional version of an oval is called an ovoid.

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.

Oval (noun)
A shape rather like an egg or an ellipse.

Oval (noun)
A sporting arena etc. of this shape.

Oval (noun)
In a projective plane, a set of points, no three collinear, such that there is a unique tangent line at each point. (A tangent line is defined as a line meeting the point set at only one point, also known as a 1secant.)

Oval (adjective)
Having the shape of an oval.

Oval (adjective)
Of or pertaining to an ovum.
“oval conceptions”

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}“
“=”
“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.”

Oval (adjective)
having a rounded and slightly elongated outline or shape like that of an egg
“her smooth oval face”

Oval (noun)
a body, object, or design with an oval shape or outline
“cut out two small ovals from the felt”

Oval (noun)
an oval sports field or racing track.

Oval (noun)
a ground for Australian Rules football.

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”