I am a travel nurse. I don't have experience as an agency/per-diem local nurse. My understanding is that you are considered a "travel nurse" if your tax residence is more than 50 miles away from the hospital. Because you will live far away, usually you will sign a 13week contract. Travelers get special tax breaks for having to "travel to work" which is the main difference between being local agency/per diem. Also as a traveler, you are generally going to work as a full time employee and have to work everyother weekend like staff members and you will set a schedule. An agency/per-diem worker can usually pick out which shifts they want to work depending on the hospital's need. You won't be guaranteed the hours like a traveler would, but I think they both make pretty good money, about $45/hr depending on the area. However the travel nurse won't get that much on a paycheck. Rather, it will be more like $30/hour with a generous tax free housing stipend. There are also seasonal jobs, or agency contracts that are set up very similar to travel jobs, the only difference is that your tax residence is within 50 miles of the hospital.
Also, agency nurses/per diem travelers usually get the same amount of orientation times (which varies from hospital to hospital) and can range between 4 hours-2days at most. Some hospitals are nicer to temp help than others. You are expected to be very independent and strong nurse when you walk in, who just needs to learn the charting and where supplies are.