I struggled with the terms "box joint" and "finger joint." Until this thread, I thought that they were one and the same.
The joint with square tabs that makes the corner of boxes is a box joint, but many people also call it a finger joint. To them, they are the same exact joint. I have used the terms interchangeably myself.
There is another kind of finger joint. This one uses interleaving fingers to join two boards into one longer board. The joint is flat. The pattern can vary, but most often it is in the form of tapered fingers that interleave together.