My customer asked if I can do an MOS and RA. RA should be risk analysis if I'm not mistaken. But what is MOS?
Acronyms and initalisms are useful shorthand when discussing a problem domain with others who share the same lexicon. However, such shorthand is highly contextual. For example, an "R.A." might mean Risk Analysis in an information security context, but a Residential Assistant in a college dormitory.
Inspect-and-Adapt Your Communications Plan
If you want to know what a customer means by a given acronym, just ask. Strangers on the Internet won't know what the client thinks a given acronym means, especially if they're using an acronym or concept in an unusual way (as sometimes happens in the real world).
Better yet, ensure that your project maintains a glossary that includes the acronyms, initialisms, and domain-specific terms that your project actively uses. This avoids a great deal of ambiguity, and can be surprisingly effective at improving project communication.