I often hear shows talked about as being some number of "cours". For example, Evangelion is apparently "two cours", while Madoka is "one cour".
But what on earth does "cour" mean? I can't find it in any dictionary!
- One of the four conventional three-month periods of television broadcasting in Japan (January to March; April to June; July to September; October to December): "Noragami" aired during the first cour of 2014.
- A portion of a television program aired over the course of one cour1: The big reveal at the end of the first cour of "Valvrave" had me on the edge of my seat!
I'm really not sure how long "cour" has had currency in English. There are attestations from at least as early as 2007.2 I think that's not too long after the term began to see usage in English-speaking anime communities, but I could very well be mistaken.
This term was probably quickly adopted because it provides an unambiguous way to refer to a roughly 13-episode block of episodes, by contrast with "season", which (as seen here) can mean many different things in different contexts.
A cour is not of precisely-defined duration, and can, in practice, last anywhere from 11 to 14 weeks (and hence, the same number of episodes), though 12-13 weeks is most common, since a 52-week year cleanly divides into four 13-week subunits (or perhaps 12-week subunits with a week off in between).
This usage of the word "cour" in English is (perhaps surprisingly) a borrowing of the Japanese word クール (kuuru), which means essentially the same thing as the English "cour".
Japanese kuuru is itself a borrowing, though the language of origin is not known with certainty. The most popular hypothesis is that it derives from French cours, cognate to "course" as in "lecture".3 Note that the English "cour" is effectively a back-formation from cours (which is singular in French), and the singular/plural distinction between "cour" and "cours" is an English innovation.
In any case, the path "cour" took on its way to English is decidedly opaque, and so it is no surprise that it doesn't show up in English dictionaries.
1 The definition at top is my own creation, but I do believe it to be correct and reflective of the way the word "cour" is used in practice. I guess it's good enough for Wiktionary?
3 I'm not sure why this is the standard etymological theory - what does a "course" in the sense of "lecture" have to do with a block of television programming? - but there you have it.