Usually, these are specialty admission programs housed and administrated independently by a larger university.
They have higher (often-- MUCH higher) admission standards, and may be extremely competitive to get into. Students in honors colleges may have special (smaller) classes, be allowed to register before other students, etc. Students usually are expected to do undergraduate research, international study, and seminars as part of the honors program. Special advising, events, dorms, and study areas on campus are other frequent perks. The quality of the programs varies tremendously however-- so caveat emptor, like anything else in higher ed.
The nice thing is that at many flagship public Unis, the tuition differential is really small. So the programs are like the 50-60K a year "private college" experience, but at a price-tag more like 16-25K. We've opted to go this route because with a child who has interest in STEM, we were stuck looking at options of: a) very elite undergraduate schools, with elite admissions frenzy and elite pricetags to match, b) HUGE flagship unis in order to get research opportunities in areas of interest, or b) sacrificing areas of research interest to get small classes and Socratic instruction.
The Honors College DD chose as her top pick avoids A, and gets both B and C without major sacrifices in either one. Of course, they admit only about the same % as Stanford or HMC, so it isn't like we avoided all of the downsides with A, but at least it's not 55K annually, either, and the institution offers a lot of merit aid to boot, making undergraduate VERY low cost in spite of being at a flagship Uni.
