Lecture: Class consisting a large number of people (about 50). It's an informative session where you are fed with information on a subject. The information flows one-way, that means there is no real discussion, but just a presentation (oral, etc) by the lecturer. If the class is too large, it could also be broken up into smaller groups led by individual Teaching Fellows.
Seminar: Seminar is a small class consisting anywhere between 8 - 12 people. Students are expected to read up the material specified by the faculty and be ready in the class. Sometimes, a student may also take the lead to present the readings to the whole class. the class thereafter is about discussion and elaboration of ideas. It is more interactive and dialogue oriented.
Symposium: Lectures constructed around a single theme. The format is presentation + dialogue. A symposium is more public in nature and invites more people to participate. It is generally a day long or 2-3 day long where you have a keynote address announcing the theme, where each session could have a moderator and as a whole, the symposium may have a conclusion.
Colloquium: Colloquium is generally a course which goes along for a semester. Students may get credits for it by attending it. It can involve different speakers each session. Thus, its format could be seminar, lecture, etc. depending upon the strength of the class and involves a longer duration of study unlike a symposium.
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School: A building which houses activities / programs related only to study.
College: A place where different facilities like a place of study, living, eating etc is encompassed in a single building.
Campus: An organization of schools and colleges that lie together in close proximity to each other. They may also extend to include other aspects (like recreational facilities, international centres, etc.) within their geography.
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Course: Is equivalent of a topic in a subject which tries to cover a small aspect of study. Ut has credits you get for (i) attendance and (ii) course work which is generally writing or studio based.
Program: A collection set of courses make a program. Programs make up for a degree in a field.
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Assistantship: Generally assisting the lecturer/professor in tasks that are more physical in nature (menial jobs). These could include setting up projectors, arranging classes, collecting material for the class, preparing presentations, etc. Assistantships are generally paid by the hour, and are low paying positions.
Fellowship: A fellowship generally means that you assist the professor in more intellectual tasks like taking smaller groups of discussions for a larger class or also checking papers written for a class, etc. Fellowships are paid in lumpsum and are not hourly jobs. Sometimes, one may not even be required to teach or work for the class in case he/she gets a fellowship. It could just be an award of a fixed amount of money.
This post can also be read at http://yalestories.wordpress.com/2012/08/31/glossary-of-terms/