Refers to the Korean language, typically as spoken in South Korea. In contexts where a distinction is needed, North Korean is 北朝鮮語 or 朝鮮語.
韓国語を勉強しています。
I'm studying Korean.
このドラマは韓国語で話されています。
This drama is spoken in Korean.
She speaks Korean very well.
I'm studying Korean at university.
You can read that news in Korean.