focal means it's in a small area. Colitis means inflammation of the colon. Active means it is currently inflammed.
You should be able to google it and have sites come up; I did.
To paraphase what I read, if you are taking an NSAID, stop because it could have caused it.
It can be caused by a bacterial infection. In the study I read about, there were other possible causes, including irritable bowel. So you should ask your questions at a follow-up appointment. But the good news from the study was that it was usually treatable or would heal on its own, depending on the cause, and it didn't seem to be linked to a chronic type of colitis.
Well, I googled it and couldn't find anything that I understood. But thanks for the meaning. Well, when I went to the doctors I asked what kind of colitis I had and he circled that word focal active and pretty much told me to look it up. He was quite rude. I'm not going back. I need to find a better gastro doctor.