Salary means you get paid a certain amount of money every year but everything else is defined by your contract: You might not have to come in at all if your contract doesn't stipulate that, you could even literally be paid to do nothing or you could be on call 24/7 or anything in between.

This is not the same thing as contractors, who are not employed by the company and bill for their work at an hourly rate. Salary is more stable income usually with decent to good benefits in the US and can work any number of hours (or lack thereof). Contractors can make more per hour, but still have to cover their own medical, dental, retirement, etc.