it can be one of two things in my experience. it can be the physical housing of your amp head, power conditioner, etc...but there are also effects racks. i don't like racks. with them people can just dial something in and make all these super-polished effects. i think it takes the human touch out of the guitar playing. i really just like pedalboards, those are great to have. but all the massive fx racks turn people into annoying 'rack and rollers'.
so yeah.