Asked as "What is accumulator bet?", the answer starts with one ticket. A parlay, called an accumulator in many places, joins several picks into one bet. Every leg has to win for the ticket to pay, and the odds of the legs multiply, so a small stake can return a large sum. What makes the format attractive is the same thing that makes it hard: each added leg lowers the chance that the whole bet comes in.
A push, where a spread or a total lands exactly on the line, does not win a parlay and does not lose it. Most books treat a pushed leg like a void one: it leaves the ticket, and the parlay pays on the legs that remain. To define a same game parlay simply: several picks from one match on one ticket. Because those picks are linked, the book prices the combination itself, and its margin on a same game ticket is wider as a rule.
Can parlays be profitable over a long run? Rarely. Each leg carries the book's margin, and multiplying legs multiplies the margin as well, so a four leg accumulator hands the house far more edge than four single bets would. Accumulator bets are worth it as entertainment priced in advance, a small stake on a long shot. Anyone who treats them as a way to earn is paying the widest margin on the menu.
Multiply the stake by the decimal odds of every leg; three legs at 2.0 each turn one unit into eight.
A bet that reverses the usual logic and pays out when at least one of the selected legs loses.
A small stake treated as entertainment money priced in advance, since multiplied margins make accumulators a poor way to earn.
The whole ticket is lost at once, whatever the results of the other selections turn out to be.