"sjmmv" doesn't match any well-known acronym or term I can identify. Could you give me a bit more context? For example:

• Where did you see it (a file name, a code, a license plate, a username)?
• What field is it from (tech, finance, gaming, etc.)?
• Is it possibly a typo for something else?

With a little more info I can help you figure out what it means.