Well, you should probably read the Wikipedia article on gambling.
Odds are the way that a bookmaker defines what the payoff will be if you win.
So if it’s a horse race, and you bet on the horse with 1/1 odds, then if you risk £5, and that horse wins, you get your initial wager back, plus £5. If it were 10/1 then you would win £50 on a £5 wager.
I think the 2.0 thing just means they payoff (total amount returned) would be 2 times what your initial wager would be, but I don’t think bookmakers ever notate it like that.
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