What is "/ /" used for in a sentence?

I received the following sentence from someone which read:

"Is there a reason I /wouldn't/ want to go?"

What is / / used for in this context? My guess is a textual representation of upward intonation for emphasis but I cannot find anything on it.

Note: I've seen many articles that say "it's for a programming comment." I'm a programmer and am aware of that but it doesn't seem to be used as a comment in this case.

In the sentence quoted, I would interpret the marks as an indication that the enclosed word would be printed in an alternative typeface—italic or bold—if the layout conformed to conventional orthography, where the sentence would be laid out

"Is there some reason I wouldn't want to go?".

In other contexts, for example, a program listing, they might be indicative of a comment, although this might vary by the language, as different languages might use different punctuation protocols to denote a comment.

This is a common convention in text-only communication, such as Usenet, email or IRC. Without typography, some indications of emphasis are commonly used:

• _underline_
• /italic/
• *bold*
• -deleted- (rare)

(Sorry, no authoritative reference - just personal experience).

The use of // to indicate italics goes back earlier, to typewritten documents; the other forms could be created by overtyping.

Some of these conventions have influenced the Markdown used here on Stack Exchange.

That can be a letter from an old person. Many old typewriter machines had no parenthesis characters, specially in foreign languages, where they use more letters than in the English alphabet, so the standard had to be modified. So people who learned typing on those machines used the / character in place of parenthesis. Then it can mean many things still, like an alternate thought, an internal note, or anything a parenthesis can be used for.