To destroy a card is to remove it from play and put in into it's owner's graveyard. Creatures that are destroyed can be regenerated by effects unless some effect prevents them from doing so. On older edition cards the word Bury was used, but if a creature was buried it could not be regenerated.
Source: Classic sixth edtition Rulebook.
Indestructible cards cannot be destroyed without the Indestructible ability being removed.