Definition of Action
What does the term "action" mean in the world of sports betting? What is the definition of the term "action"?
In sports betting, "action" simply refers to a wager that has been placed on a game.

If somebody decides to take this bet, you would have some "action".
Another example:
Let's say that you are watching a NFL game. You decide that you really like the Broncos to beat the Seahawks and you want to wager some money on the game.
You ask your friend to recommend an online sports book as you really want some "action" on the game. He tells you about his favourite book (William Hill) so you sign up for an account and place a wager. You wanted to make a bet on the game and William Hill gave you "action."