What does every Tom **** and Harry mean? ?

It is so old there is no historical record of it's true origin

Not what 'every John Thomas and Harry D i c k' means, though one could use it as a synecdoche to mean exactly what 'every Tom, D i c k, and Harry' means, like, 'I asked every Tom, D i c k and Harry in there if he'd...' and 'I asked every John Thomas and Harry D i c k in there if he'd...' would mean the same thing, albeit possibly with different effect, like maybe 'there' is a men's changing room.

It's an old British saying. It's basically just three common English informal names used to mean any random person.

It is a term for anybody/everybody.