The quick/simplistic answer, as far as I understand it, is that colleges don’t have graduate students or programs. So by definition, one of, if not the main goal, is the education of undergraduate students.
This is what I understand the specific definition to be, but fwiw when used by many folks in the US the word college takes on a broader meaning. For instance, the institution where I received my higher ed (in the US... many years ago) has both undergrad and graduate programs, and has a reputation as a highly regarded research institution. It is also referred to by both staff, alumni and current students as a "college" - I can't think of one time I've ever heard of it referred to as a university. We also tend to ask people "Where did you go to college?" rather than "Where did you go to University?" (eta - this might be a regional thing?)
Re the question of which colleges (or universities) have great teaching - access to the teacher is in many ways as important as the quality of teaching. For my kids, it's more inspiring to be in a small class rather than a large lecture hall, and the peers in the classroom play a role in the teaching as they often take in as much or more from the discussion that takes place as they do from what's prepared for the lecture of the day. Being able to meet with a professor during office hours without having to wait in line or having to meet as a group for help is a huge plus. Are the teachers so bogged down with a large number of classes, large number of students, or research that they are not able to spend time with individual students? Lastly, teacher style is a factor that can't be quantified - two of my kids have gone to the same high school and taken classes from the same teachers and had polar opposite learning experiences simply because of the teacher's style and the way they relate to the teacher as individuals.
The good news is, (just my opinion from having been through one child's college search and in the process of another)... there are a *lot* of good options out there, especially if you attempt to go beyond the mindset of feeling it's necessary to attend one of the elite universities who prides itself on extremely low admissions rates. (please note that I'm not knocking those universities - they're amazing institutions but are often simply out of reach for even many qualified students based on the large number of applications)
Best wishes,
polarbear
