Top lane.
It's the lane which is on the top of the ''rift'' (obviously.)
The champs used in this lanes are usually fighters like Riven, Darius, Fiora...(Not op/broken champs, no, ahha.) Or tanks like Garen.
It's functions are:
Push lanes, alone or with the adc.
Dive to kill someone.
Tank the damage on the team fights.
As I said before, in this lane or in others you can use the champ you want, in top lane often we can see an assasin or an AP champ.