American odds (-110, +150), decimal odds (1.91, 2.50), and implied probability (52.4%, 40%) are three ways of saying the same thing.
Why it matters
Every matched-betting decision compares prices. To compare two books you convert both to the same format — decimal is the engine's canonical form.
Implied probability is the tell
Converting a price to implied probability shows what the book thinks the chance is. Add up both sides of a market and the amount over 100% is the book's margin (vig) — the smaller it is, the better the market for you.