On one hand, a "College" (for example, Boston College) is synonymous with a "University" (for example, University of Massachusetts). In this use of the term, it means a college of academic departments as a whole organization. Thus, a school like Boston College has everything that a University has but simply has a different name. In this context, it is likely historical naming that creates a difference rather than some trait.
With that said, there is another way the term "college" is used. It is used in Universities to create organizational structure. So, the smallest group at the university would be a "program." One step up would be a "department," and a group of "departments" make up a "college." Finally, a group of "colleges" make up the "university." Here's a tangible example from where I work.
I built a new "program" in Social Media Theory and Strategy (SMS). It offers a Bachelors degree or student can Minor in it (for example, a student could have a major in Business but minor in SMS). The SMS program is housed in the Communication Studies Department. The department offers the SMS major and minor but it also offers a Bachelors in Communication, a minor in Communication, and a minor in Performance Studies. You can see that the department is larger than the program. Now, the COM department with about 10 other departments in art, music, and media production combine to make the College of Visual and Performing Arts. Here, a College is a collection of "similar" departments. Where I work, there is also a College of Liberal Arts, a College of Education, and a College of Business. These "Colleges" combine together to make the University. Here, then, a University is a collection of colleges where each college has a focus area. In this same way, there are some smaller institutions of education that are "colleges" that are independent of a university. For example, a Technical College may have a number of majors that are all trade school subjects (heating and air conditioning repair, plumbing, welding, etc.) but the "College" doesn't have anything else (that is, there is no English department or Philosophy or Physics or Art, etc.). In this way, it is only a college and is not a university as there are no other colleges merging with it.
A college is a place of learning, where a diverse range of degree and diploma courses are offered to the students, for higher studies but only in specific areas. In general, colleges are a part of universities. However, there are some colleges which are independent and not affiliated with any university, so the college itself awards the degree and diplomas. They are smaller in size than a university and due to this reason, each and every student receives good personal attention from the faculty. They may be publicly or privately owned.
The word college has been derived from a Roman word “Collegium” which means some people residing jointly under a similar set of rules for a common purpose. In many countries, colleges are referred as ‘secondary school’.
Colleges offer three types of degree which are associate, bachelor or master and diploma of graduate and post graduate level.
Definition of University
A university is a centre of education, where numerous degree, diploma, and certificate courses are offered in various areas to the students, for further learning. There are many colleges which are affiliated to a single university, and that is why a University is also known as a collection of colleges.
The degree offered by the university is associate, bachelor, master and doctorate while diplomas are offered at graduate and post graduate level. The university has the right to confer degrees and diplomas to its learners if it’s recognised and approved by the Government of the respective country or else the degree and diploma is of no use as it lacks accreditation. They are either owned by the government or private individuals or a combination of both.
It has a huge campus, where departments of various streams like Arts and Commerce, Management, Science, Geology, etc. are located. The universities are divided into the following categories, according to their formation:
The similarity to both is that they are post-secondary institutions.
Colleges can offer degree and diploma courses but can't offer postgraduate courses. Universities offer both degree and diploma course and also postgraduate courses that can lead to a Masters or PhD.
I hope this helps.