DH - dear husband
DD - darling daughter
DS - darling Son
DW - dear wife
SIL - sister-in-law or son-in-law
FIL - father-in-law
etc
SO - significant other
DF - dear fiancee
BF - boyfriend
GF - girlfriend
Then on this site you run into a lot of abbreivations for chicken breeds too
RIR - Rhode...