'Tabulation' is the noun made from 'tabulate'. It carries two meanings, and which one you mean usually shows from the words around it.

First, the act: the work of arranging figures or facts into a table, or of counting and organising them. 'The tabulation of the votes took all night.' Here it means the process, and it is uncountable — no 'a', no plural.

Second, the thing produced: the finished table itself. 'She showed me a tabulation of last year's sales.' Here you can say 'a tabulation' and 'two tabulations'.

It is a formal, written word — reports, research papers, election coverage, statistics. In talk, people say 'counting', 'sorting out the numbers', or just 'the table'. In statistics you may meet the fixed phrase 'cross-tabulation' (often shortened to 'crosstab'), which means a table that sets two things against each other at once — for example, age down the side and answer across the top — so you can see how the two connect.