To have 'deep pockets' is to have a lot of
money at your disposal.
The origin of the expression presumably comes from the tendency of
people who have pockets to store their local
currency in them, for fast and convenient retrieval. It logically follows then that a person with a lot of money would need deep pockets to
stash it all, or may in fact be rich because they discovered a pair of
magic pants with bountiful, never-ending pockets that one can never seem to reach the bottom of because there is way too much cash in the way. Possibly
pirates or
dragons were involved in this somehow - it's hard to say, but if pressed I would have to guess dragons.
What
is clear however, is that anyone in possession of such
lucky pants is unlikely to act in a duplicitous manner, for fear of losing them to the
retributive flames of truth. This may in turn explain the origin of the term '
trust fund'.