In transverse waves, the hills are called crests and the valleys are called troughs.

Here's a breakdown:

* Crest: The highest point of a wave, where the displacement from the rest position is maximum.

* Trough: The lowest point of a wave, where the displacement from the rest position is minimum.

Remember, in transverse waves, the displacement of the medium is perpendicular to the direction of wave propagation. So, the crests and troughs are the points of maximum displacement in the wave.