What it means
Day-1 retention is the percentage of installers who open the app the next day; D7 and D30 extend the window. The curve''s shape — and crucially where it flattens — tells you whether users are sticking or churning.
Why it matters
You can buy installs forever, but if D7 retention is near zero you are filling a leaking bucket. Healthy retention makes every acquisition dirham worth more and is the prerequisite to scaling spend. Fix the retention curve before you pour budget into the top of the funnel.