Cam is the river that runs through Cambridge. If you google pictures of Cambridge (which I may have done a zillion times) you will see two things: the river and the university. The river is thus somewhat of a main character in this city. On the river Cam people punt. This is how Wikipedia explains punting:

"A punt is a flat-bottomed boat with a square-cut bow, designed for use in small rivers or other shallow water. Punting refers to boating in a punt. The punter generally propels the punt by pushing against the river bed with a pole. A punt should not be confused with a gondola, which is propelled by an oar rather than a pole."

There you go.

Here is the river. I found the picture here.