The gap between revenue you earned this period under accounting rules and cash you actually invoiced, which can stretch to 12x when a customer prepays a full year up front.
When Adobe migrated Creative Suite from a perpetual license to a Creative Cloud subscription in 2013, billed revenue grew rapidly but recognized revenue dipped because subscription fees recognize ratably over the term. The reported revenue line lagged the cash story for nearly two years, a transition Adobe documented in detail to teach analysts how to read the numbers.