In The Emperor's Blades, magic-users called leaches are able to draw from a 'well' to perform magic. Most of the time, this is called 'kenning', as in:
A leach's kenning is a dangerous thing.
Sometimes however, magic is referred to as a 'delving', as in:
A week later, I had my first delving.
I have only read the first book, and I cannot ascertain the difference between the two. Is there one, and if so, what is it?