What a good question! "Visitor" and "guest" are very similar, with a slightly different meaning. A visitor is someone who visits a place, regardless of whether they were invited (like a tourist). A guest is someone who visits a place, but they have specifically been invited (by the host, who is the person inviting them). If you were to telephone me, and I said "I cannot talk, I have a visitor at my house" it might mean the mail carrier, or a delivery person (someone I feel neutral about). If I said "I cannot talk, I have a guest at my house" it might mean the neighbors are having tea or my aunt is visiting me from out of town (someone I intentionally want to be there, and who is welcome). Many hotels and retail stores try to make the customer or visitor feel especially welcome by calling them "guests" even when they are really just impersonal visitors. The person in an American restaurant who welcomes you at the door and takes you to your table is called the "host" (for males) or "hostess" (for females). They try to simulate the "at home" feeling and make the visitor feel welcome like a guest. The phrase "be my guest" is a way of making it very clear that you are offering them something, or granting someone’s wish. You might say “be my guest!” when opening a door, and allowing someone to pass. Or if someone asks if they can have the last piece of cake, you can answer “be my guest!” to say Yes very strongly. (You would never say "be my visitor.") Also, there is an implied politeness to being a guest (because you want to be gracious to your host) so children are often reminded that they should "behave like guests" when visiting relatives (instead of being naughty like they might be at home.)

Visitor -> Someone who goes to your house to visit you, maybe just to talk a few minutes, maybe for dinner but for a short time. Guest -> Someone who goes to your house and stays there (usually at least a night)

salaam visitor is someone who comes to your house to visit for a couple of hours or so but not to stay. a guest is someone who comes to house hows to stay over a couple of days.