Income drawdown is one of the ways in which you can draw benefits from your pension once you reach age 55. With income drawdown you can take income from your pension pot and leave the rest invested to continue to grow.
There are two main forms of income drawdown: Flexi-access drawdown (FAD) and Uncrystallised Funds Pension Lump Sum (UFPLS). FAD is a more flexible way to take an income out of your pension while UFPLS is generally just used to take out lump sums.
See also our What Happens at Retirement blog post.