The word is a conjunction of Fat Dumb Lesbian Bitch. The female in question may also wear Slutty short pink pants as well as see through tops but it is a total turn off for men and women alike because she is soooooo fat and wears alot of makes up. They also like to Model there Lives on the hit TV series Jersey Shore. They may also only have one to two friends and is most likely hated by all over persons.
Look at that FDLB over there that's soooooo gross ewwwwwwww. dont you just want to punch the bitch.
Stands for Fierce Duck Lips, Bro. Often used as a comment towards the 'duck face' pose, popularized in early 21st century digital photos.
Tom: Hey, nice new profile pic.
Kevin: Right? it's my duckface pose.
Kevin: Thanks, it's all in the eyes.