Yield is the percent of admitted students who have decided to accept a college offer and matriculate. Waitlisted students do not factor into a college’s reported yield, but are reported separately. For example, this from Harvard last year: https://college.harvard.edu/admissions/admissions-statistics
Heres a good 3-part article about why colleges care about yield and what it means to them
Part 1: http://ivyclimbing.com/admissions-newsletters/understanding-admissions-yield-part-1-of-3
Part 2: http://ivyclimbing.com/admissions-newsletters/understanding-admissions-yield-part-2-of-3
Part 3: http://ivyclimbing.com/admissions-newsletters/understanding-admissions-yield-part-3-of-3