Raging debate in our household tonight about the definition of a hole (which sprang from the question of how many holes apair of pants has - my contention being 1).
Colloqually people often refer to things as a hole just as something that has a cavity, like a hole in the ground. Personally I believe a true hole is defined by a porous opening having space on either side that is greater than the passage between (the passage being the hole). Anything else is just an indentation, crevass, ditch, cavity, etc.
e.g. your nose is a hole, the top of a water bottle is a hole, a nut is a hole (a portable and convenient one) but if I take a shovel and start digging, it isn't a hole, its a ditch... until I uncover a hollow space underground, then I've made a hole that goes somewhere.
Similarly... a pants pocket isn't a hole, unless its worn out and has, well, a hole in it (you know, for playing pocket pool)