Top definition
A secret kept between two friends of any gender. The difference between a regular secret and a blood brother's secret is that a B.B.S is taken to the grave with both people.
Person 1: Hey, don't tell my girlfriend about what happened last night
Person 2: Sure thing, blood brother's secret.
by giraffe112 November 09, 2015
Get the mug
Get a blood brother's secret mug for your friend José.