ここ is one of the forms of the
これ family of words used to identify things close to the speaker. In this case it demonstrates a place. In the same way that
これ represents ‘this’,
ここ represents ‘this place’, or simply ‘here’.
The full family of words used for identification/demonstration in Japanese are referred to as こそあど言葉（ことば） (KO, SO, A, DO words). These include all of the different forms of これ, それ, あれ, and どれ.
ここ should not be confused with こっち, a similar word which is also sometimes translated as ‘here’. こっち focuses more on the direction that one is/is going, while
ここ focuses purely on ‘this (stationary) place’.