A "true friend" is someone who sticks with you(Stays your friend) in good times and bad times. The opposite to a "Fair weather friend" someone who is only a friend as long as things are going good, e.g. while you have money, are popular, etc... This is why people say that "It's only when times are bad that you find out who your true friends are."

For me a true friend is someone who would help you if you were having problems, as opposed to someone who is just an acquaintance.

Someone who is a genuine friend to you - contrasted with someone who only ,pretends to be a friend or is a a casual acquaintance of whom you would not expect genuine friendship, as in a stressful or difficult time.