Salaried employees make a set
salary instead of being paid
hourly. Traditionally, this method of payment was reserved for
professionals (in the strict sense of that word), but today it is applied to all kinds of
workers.
Being salaried usually has some benefits: You don't have to punch the clock, and it usually (not always) means you're "full-time" and receive the benefits that go along with that (health care, if you're lucky).
In my experience, being salaried usually has many more drawbacks than advantages, however. Theoretically, because you aren't being paid by the hour, you should get the same amount of money no matter how many hours you work. But somehow this only ever goes one way: If you miss hours at work you're expected to make them up, but if you work extra, you don't get paid any more.
Also, salaried employees are exempt from many labor laws. Most notably, in many places they can be required to work more than 40 hours / week and they don't have to be paid overtime.