What does bio mean in profile?

This stands for 'biography' where you give some information about yourself so that others can see if they have anything in common with you.You can tell about your hobbies,your favourite sports,what type of person you are and many other things.

It is the section online that tells something about you. Most common things that are found in Biography are Names, hobbies, Achievements, Employment history. You may also include other things that which you think best describe yourself.