In reading the [ASTD State of the Industry](http://store.astd.org/Default.aspx?tabid=167&ProductId=25316) report, I find the metrics include "Hours Used" vs "Hours Available". It states that a typical ratio would be 50 hours available for every hour used.

If I assume hours used to be the actual number of training hours received by an employee, what does that make hours available? What are these two figures and what is their significance?