A full day is defined as 8 hours a day and 40 hours a week in Germany, This means that students are allowed to work only 2.5 full days per week during the semester. This limit can be exceeded during the semester and during the summer break, however, international students should keep the annual quota in mind and make sure not to exceed the 120 full-days per year limit.
Part-time or half-days are defined as anything under the definition of a full week. So a part-time job in Germany usually is a job that requires up to 20 hours or less per week.