Technically, a toe walley is exactly what Thin-Ice said. Since that is so difficult, though, and since very few people do toe-walleys, the term has come to mean a toe loop that is entered through a mohawk, back push instead of a three turn. IE, if you skate right-handed (the more common way), to do a "toe-walley" you would do a RFI to LBI mohawk, then RBO, and stretch your left foot back to take-off.
Normal walleys, actually, though, aren't all that uncommon. Maybe its a regional thing, but pretty much every girl at my rink at one time did a walley-walley doubletoe for their jump sequence (I think its the junior test....). Eventually, everyone's spun off in different directions, walley-walley double-toe double-loop, I did a walley-walley double-flip double-loop....Either way, its actually probably one of the easier sequences you can do.