Think of an Ivy League school, your local community college, and a large state university. These three colleges and universities are looking for very different types of students and have vastly different criteria for those they admit to their programs.
Every college has a governing body made up of lead administrators who have a long-term vision of what type of college they are, disciplines and programs they want to emphasize, how the college should function financially and how they will be thought of in the academic community. When you submit your college application, these people are looking for certain skills, strengths and experiences that meet their college profile based upon your high school resume.
Community colleges admit nearly everyone who applies, giving them a large admissions funnel that accepts most students, many of whom go on to four-year colleges and universities. Your favorite state university probably has a medium-sized funnel with some level of selectivity. This means they are looking to admit certain types of students to enrich their student body, help certain programs grow, and improve alumni relations. Many people have a chance of getting in, but they won’t accept just anyone. Ivy League colleges have much more selective admission standards, giving them a tiny admission funnel, which carefully strains a small, hand-picked group from the multitudes who apply for admission.