I agree with kazbern; that's just weird.
There's a minority who can't get a definite diagnosis of Crohn's or UC because their colitis shows features of both diseases. So they get a label of Indeterminate Colitis instead. Maybe try printing out something on IC from a reputable medical site on the internet and taking it along to one of your doctors?
(It's possible to have colitis which isn't Crohn's or UC, too, to be fair: microscopic, ischaemic, infectious, etc. However, IBD is by far and away the most common cause of colitis, especially in folks under 50. If your doctors continue to proclaim it's non-specific, then I'd ask
what would make it specific and, thusly, treatable.)
Or, better yet, just hand them a copy of this article and ask them to define their terminology; they'll love you for it, no doubt :p www.ncbi.nlm.nih.gov/pmc/articles/PMC1770777/