A pensioner is someone who receives a pension: money paid regularly after they have stopped working, most often because they have reached retirement age. In British English this is the ordinary word for a retired older person living on that money — shop signs, bus passes, and newspapers all say pensioners when they mean that group. American English more often says retiree or senior. The word is not an insult, but it does mark someone as old and no longer earning a wage, and it can carry a little sympathy, because a pension is often a fixed, not very large, income. Though actually, age is not the whole story: a younger person whose working life has ended through injury can also be a pensioner. You would not call someone a pensioner just because they are old, if they are still working and not living on a pension.