ROI

ROI measures the net gain from an investment relative to its cost, expressed as a percentage.

ROI is broader and older than ROAS — ROI is a general finance concept (any investment, any timeframe), while ROAS is a marketing-specific ratio of revenue to spend. Critically, ROI is profit-based (it nets out the cost), while ROAS is revenue-based (it doesn't). A campaign can have a great ROAS and a poor ROI if margins are thin, which is exactly the trap ROAS's entry describes.

In everyday marketing conversation "ROI" is often used loosely to mean "was this worth it," which is fine casually but sloppy in a report — always clarify whether you mean the strict formula or the general vibe.