What does this triangle/diamond schematic symbol represent?

Could someone please tell me what the symbol ringed in red represents?

I know it has ON Switch pointing to it, but the symbol has other lables in different parts of the document.

Answer

It's an analogue switch: -

I has an equivalent circuit like this: -

Taken from here

Here is a more detailed picture showing its usage: -

Taken from here

Below is another picture showing the FETs in more detail: -

And here is a good article by Analog devices about them.