[tom_]

This symbol is not present on US keyboards.

[ndsipa_pomu]

I did not know that. It's on most UK keyboards

[mtVessel]

What is it called? What's it for?

[ndsipa_pomu]

I had to look it up as I don't know what it's called and it's a negation symbol https://en.wikipedia.org/wiki/List_of_logic_symbols

As to what it's for, I'd say it's great as a delimiter. I've never used it for its intended purpose.