Part-time employment is not defined by the U.S. Department of Labor, but rather the individual employer. It is a set amount of hours the company considers part-time, which can be 20, 30 or 35 hours. The employee handbook defines part-time and full-time per company policy.
Part-time employees, in general, do not receive the same benefits as a full-time employee. Again, this is up to the individual company. These benefits include health insurance, paid time off, paid vacation, sick days and sick leave. It is common for a company to allow part-time employees to be able to have a portion of the benefits offered to a full-time employee.