Annuity is a promise. It is a product one pays for now with the hopeful promise of receiving regular payments later. The most common examples are Social Security, which people pay into throughout their working lives to enjoy upon retirement, Roth IRAs and other kinds of limited-accessibility retirement funds, and the ongoing donations people make to e-girls over the internet for the hopes of instant messaging later.
Annuity is associated with long waiting periods, and the overall investment is divided into two phases: the accumulation phase and an annuitization phase.
Accumulation is precisely what it sounds like. It is the period when money is added to the product and cannot be removed without penalty.
Annuitization is the better phase because you can finally reap your regularly timed payments without issue.
Finally, GNU is a collection of free software for various purposes. If you need clarification as to why this is mentioned, please read the title of this page.