Its a TM, go to fallarbor town and head west to the fossil maniacs house in there talk to the little kid he will give you Dig.
A HM is a move is a move that can be tought to as many Pokemon as you like but the Pokemon has to be able.
dig isn't a hm move on Pokemon pearl
The Pokemon that can learn any move from TM's and HM's is Mew.
the hm move strength is found in the cave Rusturf tunnel
anything that is a ground type. some Pokemon may already have dig like Diglet so you don't have to find the hm.
Hidden Move 8.
move deleter in lilycve (end of game)
yes
youdon't defog is a hm move that is in Pokemon diamond, pearl, and platinum
Go to Lillycove City and in that town there is a move deleter who will delete any move (Including HM's) for free.
Dig is not a HM in Pokemon Platinum but a TM, it can be found in the ruin maniacs cave.
You have to teach one of your Pokemon the HM 'Strength' and use it.