What is the "CAM table?"

The content addressable memory table – CAM table may also be known as the mac address table (Cisco uses the term interchangelby – their is some debate on this.)

It is used by ethernet switches to store valuable information such as mac addresses, vlan id’s and ports.

As we can see in the table below the switch records the mac addresses of the end devices and populates the table.  

A switch operates by learning on its source and forwarding based on destination. It takes what it learns from source and adds it to its Mac address table.

If a switch needs to forward a frame it will look to see if it has that mac address in its table and forward out to the appropriate port associated with that mac address. If an address is unknown a frame will be forwarded out all ports(flooded) except the one that it came from to update the table(This is called an unkown unicast frame). 

A switch will periodically clear out its CAM table using its aging timer (default is 5 minutes) . One reason it does this is to make sure that things havent changed as well as to keep the table up to date and not bloated.