Whom does the Sanskrit word "Ṣaka" (शक) refer to?

This may be a very amateurish and naive question, but as I am an absolute novice in Steppe history, I shall proceed nevertheless.

As per local mythology in central-southern India, the festival Gudi Padwa/Ugadi is celebrated as it was the day the Emperor Ṣālivāhana returned victorious to his capital at Pratiṣṭāna after defeating the Ṣakas in around 78 A.D, which is also the zero year of our Ṣaka calendar (Also known as Indian National Calendar).

My question being that given the interchangability of the words "Yavana", "Turuṣka", and "Ṣaka", who does the term Ṣaka in this context refer to?

I'm assuming it probably refers to the Indo Scythians who invaded India in the first century anno domini.