What the heck is a "trunk number" when referring to a phone?

Question

we're trying to change our phone message at work, but the instructions refer to a "trunk number" and we have NO idea what that is and can't find out an answer.

anyone?

Answer 1

These days it would be called the national number, ie. the full number starting with a zero.

There used to be 'local' calls and 'trunk' calls.

Answer 2

It's the main incoming phone number into your PBX.