OK I'll take a shot:
here are some quick answers:
lets start with pattern. pattern is also called "precision aerobatics" or "Precision flying". the sequences are designed to be flown smoothly and are well thought out. all classes up to masters are AMA classes. the top class flys the FAI sequence (federated aeronautic international(??)) AMA also follows FAI rules as far as the planes themselvs are constructed. the must be under 2 meters wingspan and 2 meters in lenght and must weigh under 11 lbs. the "pattern" planes are pupose built within these rules and are quite unique.
IMAC is also known as Scale Aerobatics (SA). IMAC replicates the full scale aerobatic planes and sequences - International Aerobatic Club (IAC) the "M" in IMAC stands for Miniature. the planes must be scale copies of their full scale counter parts. the design rules allow for 10% deveation from scale to help our models perform alittle better in the manuvers.
TOC is the highest level of "precision flying" and is an invitational event. the competetors fly IMAC large scale planes, but their sequences are not limmited to IMAC or AMA rules. I beleive they follow FAI criteria for judging and sequence design (?) most TOC competitors fly both FAI and IMAC.
freestyle or 3D is the expresion part of flying. roughly speaking 3D means high alpha and sometimes high energy manuvers that most full scale airplanes could not execute. there are always new and exiting 3D manuvers being created and pilots doing some unbelievable things with their planes. then you can string these manuvers together along with some choreography to music and put together a "freestyle" flight routine. that routine is judged on choreography, dificulty of manuvers, originality, just like a figure skater would be judged in the olypics.
wow, thats not quite as short as I though it would be
these are (I hope) generalizations, and if Im wrong somewhere, Im sure someone will correct me
Hubb