What is the meaning of the English expression 'fits the bill'?

If something 'fits the bill' it means that it meets expectations, it is entirely suitable, or satisfactorily adequate.

For example, a person might want a new PC and would like it to have certain features, such as a DVD drive, disk burning facilities, multiple USB ports, and be within a certain price range.

If a retailer has a PC that exactly matches that specification, that new PC 'fits the bill.'

The Word 'bill' has a number of meanings, one of which is: a printed list.

In the example given above about someone wanting a PC, they would have a list (maybe in their mind) of the features they want, and would be looking for something that matches all the criteria on that list, something which 'fits the bill', i.e. the criteria list of items they have previously decided upon.