A tally is a continuous count of something, like the number of words in a document, or the number of favors your best friend owes you. To tally is to add up, like keeping the score of a game.
The word tally has to do with counting. It comes from the Latin word for “stick” because people used to keep a tally by marking a stick. Tally can be the total, or the act of adding it all up. If you count the bikers riding by, your count is a tally. As a verb, tally is used for keeping score. Two friends playing basketball need to tally the points after each basket so they don't lose track.