Which means, for example, Attack on Titan/Shingeki no Kyojin doesn't count as only one entry. It counts as at least 6 entries based on seasons/cours alone, and more if you count OVAs, specials, and recap movies.
MAL Search Result for Attack on Titan/Shingeki no Kyojin: https://myanimelist.net/anime.php?cat=anime&q=attack%20on%20...
I know weebs go nuts for for "just according to keikaku" *keikaku means plan but this one is just baffling to me.
Why use a loan word that itself is a loan word that just comes back to season?
Well, or rather, consider the following (Ascention of a Bookworm S3): a 26 episode series airs in fall and winter, making it a two-cour anime; it's not a two-seaon anime because it's actually the third linearally related show.
We could call it the second sequel instead of the third season, but this doesn't seem to happen.
It's been widely used long before Shirobako. But otherwise yeah. It's the subdivision of a season of a show (group of episodes produced together) that fits within a season of television (around 12 weeks). The options in English are too clunky or not specific enough for the context in which people say "cours".
I always get a kick of hearing people hesitate when deciding whether to pronounce it French-like, English-like, or Japanese-like.