What is the difference between an institution calling itself a "college" or a "university"? For example, take the "University College London". Is it a college? A university? Both? What does it mean?
Some colleges are universities: The Imperial College of Science, Technology and Medicine, London; University College London; these award degrees in their own right.
Some colleges are listed bodies of collegiate universities: Merton College, University of Oxford; Churchill College, University of Cambridge. These do not award degrees in their own right; the parent university awards the degrees. Some teaching occurs in college. Some teaching and research staff are attached to a college, and to a university-wide department; others are attached only to a department. All undergraduates are members of a college, and of the parent university.
Some colleges are residential bodies of collegiate universities, e.g. Bowland College, University of Lancaster; Halifax College, University of York. Teaching does not occur in college, and the parent university awards the degrees.
Some colleges are independent and part of no university: Ruskin College, Oxford; Working Men's College, London. These tend to make awards other than traditional degrees.
This is the situation for England. Other anglophone countries may have different arrangements.
In the US there really isn't a distinction any more. Traditionally, a university was a larger institution that typically offered graduate degrees (MA/MS/PhD) and had a multitude of colleges (e.g. a college of arts and sciences and a college of engineering) and professional schools (law, business, medicine, etc.) Now, lots of institutions that offer only bachelor's degrees have taken to calling themselves universities.