Google is your friend <3 http://ffxiv.consolegameswiki.com/wiki/Elite_Marks

That aside, you can figure out the names of hunts by visit each zone respectively and talking to the Hunt NPCs in each town. A Ranks and S Ranks will always reward seals and tomestones for killing them, while B ranks are only killed for the weekly hunt log.

A ranks usually require a party ore more to kill. S ranks are like mini raid bosses and require quite a lot of people to kill. B ranks are easily soloable with a chocobo.