Question: What is the type `+` (obtained, for example, with command "whattype(_i+_j)")?

Reading another question today I discovered that I can use syntax like

a := 2 _i + 3 _j

b:= _i - _j

a+b  

Maple computes the sum by vector component. This is very useful, and it prompted me to start reading the Multivariate Calculus Study Guide. I am still going through it but haven't seen this particular notation yet. When I check the type of a above I get a result that sort of looks like `+` but actually it seems to be tilted to the right (so I guess it is italicized and represents some symbol).

What is this type?

I don't find much searching online, and I did see this page that says 

"Any symbol beginning with an underscore (_) is effectively reserved for use only by library code. It is not available to users. Failure to observe this rule can lead to unexpected results."

Edit: After a bit more looking, looks like my example code is using notation available from the Physics package, which I am now reading a bit about (but it is not clear to my why this package is used since I am not importing it explicitly).