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1.
Best Friends In Love

A relationship between cute little southern girls.
Man, those girls are BFIL.
by Hilliary January 17, 2006
 
2.
Noun. Short for Best Friend in-law. Pronounced biffle. The spouse of your best friend or your spouse's best friend.
Congrats for marrying my best friend; you will make an excellent BFIL.
by Kit17 April 03, 2014