Learn Hardcore Afrikaans: Die huurtermyn is kort.

It does not change for gender, because Afrikaans nouns do not have grammatical gender the way some other languages do.
It can be used with both singular and plural nouns.
It is usually pronounced roughly like dee, not like the English verb die.

So die huurtermyn means the rental term / the lease term.

Why is huurtermyn written as one word?

Because Afrikaans, like Dutch and German, very often forms compound nouns by writing them as one word.

Here:

So huurtermyn is a compound noun meaning something like rental term or lease term.

This is very normal in Afrikaans. English often writes similar ideas as two words, but Afrikaans frequently joins them.

What does is mean, and is it only for singular subjects?