This is where a character is thinking about something (usually critical to the plot) and is pacing the floor as he or she is doing it. Often they will walk back and forth across a room, but occasionally they will walk in a circle instead.
One example is the Spongebob episode where Spongebob and Patrick are playing imagination games in a box and Squidward is seen pacing the floor trying to figure out how they are making the sound effects he is hearing.
Another example is in the Great Mouse Detective where Basil is pacing the floor and smoking his pipe while thinking about the case.
More examples appreciated!