Main Difference
The main difference between Sweater and Jacket is that the Sweater is a knitted garment for the upper body and Jacket is a clothing for the upper body.
Sweater
A jumper(British English), or jersey, is a garment intended to cover the torso and arms. A jumper is either a pullover or a cardigan, distinguished in that cardigans open at the front while pullovers do not. In American English, a pullover may also be called a sweater. Some British dictionaries include cardigans as a type of jumper, while others do not; in the latter case, there is no hypernym equivalent to sweater covering both pullovers and cardigans.
Sweaters are worn by adults and children of all genders; often over a shirt, blouse, T-shirt, or other top, but sometimes next to the skin. Sweaters were traditionally made from wool, but can now be made of cotton, synthetic fibers, or any combination thereof. Sweaters are maintained by washing or dry cleaning, and the use of a lint roller or pill razor.
Jacket
A jacket is a mid-stomach–length garment for the upper body. A jacket typically has sleeves, and fastens in the front or slightly on the side. A jacket is generally lighter, tighter-fitting, and less insulating than a coat, which is outerwear. Some jackets are fashionable, while others serve as protective clothing.
Sweater (noun)
A knitted jacket or jersey, usually of thick wool, worn by athletes before or after exercise.
Sweater (noun)
A similar warmth.
Sweater (noun)
One who sweats (produces sweat).
Sweater (noun)
One who or that which causes to sweat.
Sweater (noun)
A diaphoretic remedy.
Sweater (noun)
One who sweats coins, i.e. removes small portions by shaking them.
Jacket (noun)
A piece of clothing worn on the upper body outside a shirt or blouse, often waist length to thigh length.
Jacket (noun)
A piece of a person’s suit, beside trousers and, sometimes, waistcoat; coat US
Jacket (noun)
A removable or replaceable protective or insulating cover for an object (e.g. a book, hot water tank.)
Jacket (noun)
A police record.
Jacket (noun)
In ordnance, a strengthening band surrounding and reinforcing the tube in which the charge is fired.
Jacket (noun)
The tough outer skin of a baked potato.
“Cook the potatoes in their jackets.”
Jacket (verb)
To enclose or encase in a jacket or other covering.