A cycle of chemotherapy means the duration of time (e.g., the number of days, weeks, or months in the time schedule) that the particular treatment is given at a specific dose. Although a cycle of chemotherapy can be as short as one day, most cycles of chemotherapy encompass several weeks to a month.
For some types of chemotherapy, a cycle of treatment is given, followed by a resting period in which no chemotherapy is given (in order for normal cells to be replaced and strength to be restored to the body), followed by another cycle of treatment.
A course of chemotherapy is the number of cycles of chemotherapy that constitute a complete chemotherapy treatment. Typically, 4 to 6 cycles of chemotherapy constitute a course of chemotherapy.