a RIMM is the name trademarked by Kingston and is used of a memory module that utilizes Rambus/RDRAM Memory. The letters stand for "Rambus Inline Memory Module", in the same manner as SIMM and DIMM.
The standard (desktop) RIMM has a 184-pin connector, and a Small Outline SO-RIMM module has a 160-pin connector for mobile and embedded applications.
To use the term 'RIMM', you must pay a licensing fee to Kingston, so most manufacturers will simply use terms like 'Rambus Module', etc., similar to the FireWire Vs. IEEE 1394 Vs. iLink debacle.
Note: RIMM does stand for "Rambus Inline Memory Module", and I can prove it: Go here (http://kingston.com/japan/about/wnew/wn981118.asp) and find the line where it says RIMM = Rambus Inline Memory Module in the first paragraph.