The Apollo program conducted 14 lunar-surface EVAs, commonly called moonwalks. They took place during the six successful Apollo landing missions: Apollo 11, 12, 14, 15, 16, and 17.
The missions became progressively more ambitious. Apollo 11 had one surface EVA; Apollo 12 and Apollo 14 each had two; and Apollo 15, 16, and 17 each had three. Adding those totals gives 1 + 2 + 2 + 3 + 3 + 3 = 14. Across these outings, 12 astronauts explored the Moon, deployed experiments, photographed geological features, and collected samples.
A frequent source of confusion is counting every Apollo EVA, rather than only EVAs performed on the lunar surface. Apollo 9 included a spacewalk in Earth orbit, and Apollo 15 command module pilot Al Worden performed a deep-space EVA while returning to Earth. Those activities are not lunar-surface moonwalks, so they are excluded. The total is therefore 14 for the precise category used in this question.