In practice
There is no target percentage to hit. Write the page for a reader and the term will appear at a natural rate.
Use density only as a diagnostic on pages that read badly, where it usually confirms over-optimisation.
Why it matters
It was a real ranking heuristic decades ago and is now mostly a symptom to watch, not a lever to pull.
Chasing a number produces text that no reader finishes, which costs more than any keyword gains.
Related terms