Genre

Genres are formed shared literary conventions that change over time as new genres emerge while others fade. As such, genres are not wholly fixed categories of writing; rather, their content evolves according to social and cultural contexts and contemporary questions of morals and norms.

The Ancient Greeks  categorised all their writing into Epic, Comedy and Tragedy but we now have a bit more nuance and variation between our genres. 

Studying genres helps us identify shared characteristics and conventions, and allows us to emulate these in our own writing.