The Dictionary of Insurance Terms and Definitions
An annuity's life is divided into two periods: the accumulation phase and the income phase.
The accumulation phase (a.k.a. deferment period) is the time during which the annuity owner is not yet receiving a pension from the annuity. During the accumulation phase, the annuity owner pays periodic premiums into the annuity, and the annuity accrues interest.
Immediate annuities have no accumulation phase to speak of because they begin to issue a pension after the first (and only) premium payment. Accumulation phases pertain, rather, to deferred annuities.
As a rule, the owner of a deferred annuity can perpetuate the annuity's accumulation phase for as long as he/she wishes (so long as he/she can keep meeting the minimum premium requirements). When the owner chooses, he/she can end the accumulation phase and begin receiving the annuity's pension.
An exception to this rule is a CD-type annuity, for which the accumulation period is fixed.