Its just a complicated word for something very simple.
For instance, If you worked for a company for 40 years, then you might suppose to get a pension of 40/80ths of your final salary.
So, final salary was say, £40,000 pa, you would then get a pension of half, ie £20,000 pa. If you worked for 30 years, then the formula would be 30/80ths of your final salary......£15,000 pa.
There were other types of schemes but this is how they would all work......your pension would depend on your final salary and the time worked.
Be aware though, that these type of pensions schemes are rare beast these days !