· -- a binary operator, usually used for dot product

This operator may be used as a binary operator in an expression like x·y. The user may install binary methods for handling such expressions with code such as

         X · Y := (x,y) -> ...

where X is the class of x and Y is the class of y.

To insert this character in Emacs, you may press C-x 8 RET or M-x insert-char and then enter "middle dot" in the minibuffer.

Alternatively, you may press C-x RET C-\ or M-x set-input-method and then enter "TeX" in the minibuffer. Afterwards, typing "\cdot" will input the character. You may then toggle the input method using C-\ or M-x toggle-input-method