Giant cells are basically macrophages. Macrophages are the immune cells that "eat" foreign particles like bacteria to neutralize them. In a nutshell...when you get a long-standing inflammatory response, the macrophages fuse together, and it becomes one enormous macrophage with multiple nuclei, aka a giant cell. This is seen in tuberculosis infection, which is a type of chronic granulomatous inflammation, similar to Crohn's disease.
Here's something from Wikipedia.http://en.wikipedia.org/wiki/Giant_multinucleated_cell
Add: It just means you had a chronic inflammatory process going on.