If your pension is paid before your Normal Pension Age (NPA) it is likely it will be paid for more time than was originally intended. Your pension is adjusted to take this into account.
This means your pension is reduced, to take account of the extra time it is expected to be paid.
The factors are worked out by the scheme actuaries, using assumptions such as life expectancy.
The pension you have built up to the date you retire is adjusted by the factor according to your age and how early you are taking your benefits.
The easiest way to see the reduction that is applied is to use the retirement modeller in the Pension Portal, which calculates this for you.