Productivity – please explain

I am continually confused and bemused by the word salads that describe productivity. As one of the nation’s nobodies, I’d like to understand how it is derived. Once I thought it related to the output versus cost of input. That seemed clear when describing manufactured products. But how does it describe other industries? Describing the output of white-collar workers as production seems unfeasible, so how is it measured? Similarly, how can you measure the productivity of politicians? When more generic terms are used to create a national standard of output, it hides the fact that it is lower-income earners who will bear the consequences more so than those on high incomes. Perhaps I have read the tea leaves incorrectly, but us nobodies feel we are being played by a system that is not exactly fair.