A line of -150 / +130 means the favorite costs $150 of risk per $100 of profit, while the underdog returns $130 profit per $100 staked. The gap between the two numbers is the vig. Moneylines are the primary market in baseball, hockey, soccer, and combat sports, and the secondary market (behind the spread) in football and basketball.
The moneyline is market key h2h in ParlayAPI, matching the-odds-api's convention, so existing integrations work unchanged. It is the most liquid, most widely quoted market per event - the default market on the odds endpoints and the reference market for CLV grading. Full catalog: /v1/meta/markets.