Part-time study is taking fewer than 54 points (usually three papers) in a single semester, or fewer than 108 points (usually six papers) in any given year. As a part-time student you are not normally eligible to receive a student allowance, and you will take longer to complete your degree.
International students should check with the International office to determine if they're eligible to study part-time. Typically, a student visa doesn't permit part-time study.