Voluntary Accumulation Plan
  
See: Accumulation Plan.
This process describes how a lot of people save for retirement...slowly putting a little away (possibly in irregular intervals), trying to build up a nest egg.
You might not have enough extra from your paychecks on a regular basis to put away for retirement each month. However, every time you save enough to make a contribution, you put a little into your favorite mutual fund. So you contribute the funds of your own volition (it’s not done automatically) and, over time, you build up an increasing retirement savings in a mutual fund. Voluntary accumulation.