Der See - the lake
Die See - the ocean
Die See - the ocean
het meer - der See - the lake
de zee - das Meer - the sea
I don't remember being taught "die See" but I also dropped my German course after one year (which I now regret). Anyway, I always thought this was an interesting development in our languages.
The English word "sea" is also sometimes used in this sense, but it's less apparent since "the" carries no gender: "He liked living close to the sea." - doesn't really refer to a specific sea or ocean even though the definite article has been used. (I'm happy to be corrected if this is an ungrammatical sentence since I'm not a native English speaker)