CM - there is a thread under the annoucements section, called Messages for Moderators and Forum Help (if i was any good, or able to, would post the link for you) but, the first sticky on there is "Common Forum Jargon, etc" That will be able to answer most of your questions. I spent a few days on here with no idea what any one was talking about, till i stumbled across that thread.
But - SIL is Sister In Law, DH - Darling/Dearest Husband, BFP - never can remember exact what that is - but it means postive wee test, or similar.
NT is the term for the Nuchal fold thickness test, and CVS is Chorionic Villus Sampling.