To 'cast on' is to begin knitting. The only other option is to crochet a chain from your yarn and knit into those stitches- but that is still a foundation row and would be called a 'cast on'.
The word 'cast' has various meanings, from the Bronze Age first casting of molten metal to the Biblical reference to judging others- 'casting the first stone'. All the contexts refer to a foundation, the first that then leads to more. And that is probably how it becomes the term that we use to describe the first line of stitches on a needle that leads to more knitting.
So many methods have been explored and invented over the years. Maybe a few techniques began in various places as humans began making cloth and as time went by misinterpretations or purposeful new nuances began to show and we now have books which will show us how to cast on in hundreds of different ways.
This life has so many interesting complications, let's leave a few complications to those who really desire them. I just want to knit, not know how to start knitting in 200 different ways! So here are the first four methods that I suggest for beginner knitters and the four that I use most often.
The Knitted Cast On