Reddit codified an interview format called "AMA," or Ask Me Anything, whereby a million people ask questions and the ones with the most upvotes get answered. Sometimes these are with celebrities (so, "I am Tom Hanks, AMA!") and sometimes they're with various specialists. In the latter case, it's standard to add a second "sounds-like-A-M-A-but-isn't-actually-related" term, IAmA, which is just a smooshing-together of the words "I Am A." (So, "IAmA Professional Escort, AMA!")
Really, the title of this thread should use "AMA" instead of "IAmA;" because all IAmAs are AMAs, but not all AMAs are IAmAs.
*falls into an IAMAMMAAMAAAAAMMAMAMMMIAMAIMA trance*
For what it's worth, I've always thought having two different concepts linked by such similar-seeming terms was ungainly, but it is what it is.