I received a letter about funding that describes a 25% TAship. What does this mean?

The percentages listed on funding letters are based on a 40-hour work week. Graduate students are only allowed to work at the University up to a maximum of 50% (20 hours per week). Most often, our graduate students receive teaching assistantships for 25%, which equates to an average of 10 hours per week over all 11 weeks of the academic quarter. That usually includes the time spent attending the class itself.