That symbol is called a 'forward slash.'

I've hear it referred to as an oblique, and as a slash in actual conversations. In a written grammatical context the oblique means (And or) so 'ketchup / mustard' is ketchup and or mustard. Most people do to the practice of spelling out web addresses will say slash. In essence forward slash is correct, but I've just never heard it. I have heard people say back slash, and slash, and in that one business writing course, I took, I heard it identified as an oblique. HOWEVER, keep in mind, no one is going to know what you are talking about when you say solidus or oblique or a scratch comma. You SAY slash if reading it outloud in writing and if your are reading math equations 8/4 that's "8 DIVIDED by 4" or '8 OVER 4.' and in music 4/4 is four four time. Long story short SLASH or over.

Most commonly, it is called a "slash." If it is necessary to distinguish it from \, then "forward slash" versus "backslash." It has other names, but they are obscure and rarely used. When it is being used to show a fraction, such as 1/3, the correct technical term is "solidus" but I don't think I've heard anyone say that word aloud. In typography, in a set of type, it can also be called a "virgule."