What the hell is Silicone Oil anyway?

I've Googled it and it appears to be used in a lot of beauty products, as hydraulic fluid and other weird stuff.

It appears to be kind of a "Not really an oil" kind of oil.

Why would you want to use that?

I use moly grease or motorcycle chain lube for springs and pistons and motor oil or 3-in-1 type oil on external pivots.

Never seen the need for anything else.