What does octave mean in music term?

An octave is a stepping stone, of sorts.

On a viola, their are multiple notes that play 'a'.

On the G String, first finger is 'low a'

On the A string, open is 'a'

They are separated by an octave.

An octave is the distance between two of the same notes.

To play a two octave scale, start with first finger D on the C String and end with Third finger D on the A string.

The Viola has four strings: A, D, G, C. C is the lowest.