I’d suggest ‘la fac’, short for ‘faculté’, and similarly vague/indeterminate.

Si je comprends bien, un College américain peut être à peu près n’importe quelle structure proposant de poursuivre des études supérieures (si la question porte sur un autre sens du mot, il vaut mieux le préciser). Dans un contexte français on parlerait aussi d’études post-bac. Du coup, la réponse à la question est multiple (et dépend très probablement du pays francophone considéré… je ne réponds que pour la France).

L’équivalent le plus évident est l’université, ou plus familièrement la fac. A l’intérieur de l’université, on trouve les UFR (anciennes facultés), qui correspondent peut-être davantage au sens administratif de college : une unité de formation et de recherche dans un domaine (par exemple la biologie, le droit, etc). On trouve aussi les IUT.

Mais il y a aussi tout un tas de structures de formation post-bac (et qui à ce titre pourraient rentrer dans la catégorie College) qui n’ont pas forcément d’équivalent américain : les grandes écoles (écoles d’ingénieur, de commerce, etc), les classes prépa (qui préparent au concours d’entrée des grandes écoles), des écoles spécialisées (études infirmières,etc), les STS (qui dispensent un enseignement plus technique)… J’en oublie sûrement.

Concernant les collèges et lycées français : les collèges accueillent en gros les élèves de 11 à 15 ans et correspondent à peu près aux middle schools ou junior high schools. Les lycées correspondent à l’étape suivante dans le système éducatif, c’est-à-dire les high schools, en gros de 16 à 18 ans, et préparent au fameux bac ou baccalauréat qui permet d’accéder à l’enseignement supérieur.

L’équivalent français du mot « College » est l’Université.
L’équivalent en France du « College » américain est l’Université aussi.

Fondamentalement, les Universités et les « Colleges » aux États-Unis sont la même chose, mais (en même temps) il y a quelques différences qui dépendent du contexte…

It really depends on how it’s being used.

Technically, in American English, the terms “college” and “university” refer to different types of institutions (both are higher learning beyond high school). Both institutions can offer 2 year Associates degrees, 4 year Bachelors degrees, and Graduate/Masters Degrees.

A university can have it’s own smaller “colleges” (or departments) that each make up a university.

At the same time, a college can be an entity unto itself without being a part of a university and would be functionally equivalent to a university.

Within a college, there are “schools” (or departments) that make up the college, so those “schools” are the equivalent of a university’s “colleges”.

Then you add in this complication: Most Americans use the words “college” and “university” interchangeably to refer to the same thing in everyday conversation. So if you say, “I’m going to college”, that’s essentially the same thing as saying ”I’m going to attend a university“. It doesn’t really matter (and no one really cares) whether the title of the school you attend is “Centenary College” or “Louisiana State University”. They practically accomplish the same purpose and you can get the same degrees with the same respect from both.

So, colloquially, University = College as overall institutions of learning.

And within each of those, College = School as different departments of learning (business, art, science, etc).

But if you want the most accurate description, there is a good one on the Free Dictionary which reads as follows:

The term college is a general one that encompasses a wide range of higher-education
institutions, including those that offer two- to four-year programs in the arts and
sciences, technical and vocational schools, and junior and community colleges.

The term university specifically describes an institution that provides graduate and
professional education in addition to four-year post-secondary education.

Despite these distinctions, the terms college and university are frequently used
interchangeably in the United States.

College (American) = Université (French).

Highschool (American) = Lycée (French).

Since other people have described usage in France, I’ll talk about Canada.

In Quebec, le collège is a stage of education that’s intermediate between high school and university (from 17 to 19 or 20 years of age). It is compulsory to obtain a two- or three-year college diploma before entering university. Public colleges are also called cégeps. For francophone institutions in Ontario and elsewhere in Canada, the word tends to be used as an equivalent of the English junior college or community college, which generally offer the first two or four years of postsecondary education. The word Collège can also be applied, mostly outside Quebec, to a relatively independent unit of a university. (For example, the “Collège universitaire de Saint-Boniface” – known since 2011 as the “Université de Saint-Boniface” – is part of the University of Manitoba.) The term collège is never applied to whole universities anywhere in Canada, however. Those are called universités.

But alongside this usage, as a holdover from an earlier time, many private high schools in Quebec (Grades 7 to 11, ages 12 to 17) use the word Collège in their names (as in “Collège Saint-Louis”), even though you would seldom refer to them as “un collège”. This is analogous to the situation in English – it makes perfect sense to speak of the private high school called Lower Canada College, but you’d rarely call it “a college”, and you’d never say its students were “in college”.

Canadians are generally not familiar with the way the word collège is used in France.

The word lycée is not used in Canada, except to refer to foreign institutions that go by that name. The term école secondaire is used to refer to high schools in Canada and also abroad, whenever a specific foreign term isn’t used. So you’d speak of ” les écoles secondaires chinoises”, for example. Although a Quebecer might well say “les lycées français”, much as he would say “les grammar schools britanniques”, if someone ever said or wrote “les lycées chinois”, you’d know they were a European French-speaker. Certain public high schools in Quebec are called polyvalentes, mirroring the British term comprehensive.

Contrary to usage in France, you can’t use the phrase “la fac” to refer to university in general or to a particular university. In Canada, it refers solely to a faculty of a university, as in “la fac des sciences”.

The word baccalauréat means a bachelor’s degree from a university, not a secondary school diploma as in France. So in Canada, you can get “un bac en génie mécanique”, for example. In this respect, the present usage of France represents a change from an earlier state of affairs when a baccalauréat was always a university degree. On this, I believe Canada and Switzerland still agree, and I’m uncertain about Belgium.

As a result of the existence of the college system in Quebec, bachelor’s degrees usually last only three years, not four. This distinguishes Quebec from the rest of Canada and the United States.