What does "odds" mean in gambling?

In gambling, “odds” of 7:1 means you have an 88% chance of losing. For example, in 8 cards, there are 7 Kings and 1 Ace; you get 1 chance to pick the Ace.

Odds @ Wikipedia
Excerpt: The probability of a random day of the week is a Sunday is ‘one-seventh’ (1/7). A bookmaker may (for his own purposes) use ‘odds’ of ‘one-sixth’, but the overwhelming everyday use by most people is odds of the form 6 to 1, 6-1, 6:1, or 6/1 (all read as ‘six-to-one’) where the first figure represents the number of ways of failing to achieve the outcome and the second figure is the number of ways of achieving a favorable outcome: thus these are “odds against”. In other words, an event with m to n “odds against” would have probability n/(m + n), while an event with m to n “odds on” would have probability m/(m + n).