The cult board
There are four cults in Terra Mystica that you can gain influence in: fire, water, earth, and air.
You gain influence whenever you build a religious building while gaining a favor tile, or when you send one of your priests to the order of a cult, i.e. when placing him on a free space below the cult tracks.
At the end of the game, you may get victory points if you have advanced far on a cult track. During the course of the game, you may gain power for advancing on the tracks. It is quite beneficial to invest into the cults.
Only one player can advance to space 10 of a cult track. However, you need to found a town first each time you want to do so.