It's by moneyline if you're betting the moneyline, and it's by runline if you're betting the runline.
Example: Boston is -160 ML and Cinci is +130 ML, you parlay them together, $100 to win $274.
If you bet runline, say Boston -1.5 runs -110 and Cinci +1.5 runs -110, parlay them together and it would be $100 to win $265. Of course, those numbers/runlines are hypothetical.