A custom is a behavior adhered to by a group of people on a regular basis. Example shaking hands when greeting people, serving afternoon tea in Britain, or sending cards as a "Thank you". These are things done on a regular basis in an agreed upon manner. A tradition is a behavior adhered to a group of people on specific occasions that occur regularly. Examples include Holidays, wedding decorum, and rights of passage with age. These are things one on specific defined occasions in an agreed upon manner. The basic differance between the two being timing. A secondary but related differance is how long it takes to establish a custom vs a tradition. We can create a new custom right now. If you and I agree to a new secret handshake the second time we do it, it becomes a custom between us. A tradition however, must be repeated over a long period of time to be considered such.