Question

In literature, what is a subject?

Answer 1

The subject of a sentence is the do-er of the action. For example: Sam drived a car.

"Sam" is the subject
"Drived" is the verb
"A" is an indefinite article  
"Car" is the object, because it receives the action.

Answer 2

The subject is basically the main person or thing. A subject is a noun (person, place, thing, etc.). The sunject is what is doing the action