

These are some abbreviations commonly used on the boards to describe others in terms of their relationship with you intead of using their names.
BM = bridesmaid (but in certain context could mean best man)
DH = dear/darling husband DW = dear/darling wife
FI = fiance/e
FBIL = future brother-in-law
FFIL = future father-in-law
FMIL = future mother-in-law
FSIL = future sister-in-law
MOH = maid of honor