n. — Education
a short, intensive university term that takes place in the spring or summer, and that condenses 13 weeks of material into five or six weeks.
COD-2 states that intersession means "a short university term, usu. in May and June" in which 13-week course content is studied in five or six weeks (see COD-2, s.v. "intersession" (1), which is marked "Cdn"). COD-2 lists a second meaning as "US", and defines it as "a short period between university terms, esp. in January". However both the supposed Canadian and US meanings are used in the US (see, e.g. the 2007 quotation from The New York Times in which it is clear that intersession refers to an intensive course in January). This can also be seen in the general, non-time related definitions in W-3, which defines the term as "a period between two academic sessions or terms sometimes utilized (as in an adult education program) for brief concentrated courses" and AHD-5, which uses the more concise "the time between two academic sessions or semesters".
The earliest found citation dates to 1920, from the US Christian Science Monitor newspaper, and appears to refer to the supposedly Canadian meaning of a study period in May or June. Internet domain searches indicate that intersession is most prevalent in the US today and is much more rarely used in Canada (see Chart 1).
- It appears that both meanings are found in the US and in Canada. In Canada, intersession has given way to terms such as "summer session" or the like to refer to the courses held in the spring (May or June) or in the summer (July and August).
- 1944  Seminar in Social Research. - Discussion of and practice in research methods. Preparation of studies. Two hours a week. During Intersession and Summer Session. 
- 1964  There will be 50 students for this year's internship, which begins with intersession classes May 14 on the Saskatoon campus. 
- 1972  Students receiving them completed degree requirements during the May-July intersession during the 1972 Summer session or over the summer
months. 
- 1990  Students would have gained field experience and learned about the island from "a geographer's point of view," said Alan Phipps, department head. After their return they would have prepared a major paper for a six-week intersession course at U. of W.
"I have just a few fourth-year courses to go and the university isn't offering any of them in intersession (from May to June) or in summer, except for the St. Vincent one," he said. "If I could do one course in the summer, that would leave me four courses and a thesis, and I could graduate by January." 
- 1998  Campus and city police are investigating violent anti-female and racist graffiti at the University of Western Ontario. [...]
The messages were sighted in at least a half-dozen locations on building and pathway walls during May and early June but are believed to have occurred in mid-May during a lull between the end of regular classes and beginning of intersession. Police believe one person did the work. 
- 2004  Harry did not have a strong formal education but he was very intelligent. His work included writing two books related to Metis law and culture. He also taught Metis studies and politics during intersession and summer school at the University of Saskatchewan in 1994. 
- 2007  [MATH 096 covers a lot in a short time, mostly 9th- and 10th-grade material eight hours a week for six weeks. "You can't afford to miss a class," George McCormack, who teaches it at LaGuardia Community College, in Queens, warned his students as the intersession intensive revved up early last year.] 
- 2007  That was the message from Northern Lights College instructor Patrick Michiel, in an interview outlining the details of a new sales course, Management 207: Professional Selling, to be offered in the May-June Intersession term at NLC. 
- 2014  "The program runs at this time because there are two parts to it," he said. "One is the study abroad course they take with me, the other is the tutorial course they take with their Oxford tutor. My course is similar to an intersession course at STU, we have class four days per week." 
Images:
Chart 1: Internet Domain Search, 15 Aug. 2013