Final answer:
Basal body temperature (BBT) is the lowest body temperature during rest, usually when asleep. It rises slightly and stays high after ovulation has occurred. However, BBT cannot predict when ovulation will occur and is not an effective form of contraception.
Step-by-step explanation:
Basal body temperature (BBT) is the lowest body temperature during rest, usually when asleep. To accurately measure BBT, it is recorded immediately upon awakening in the morning and before any physical activity has occurred. BBT rises slightly and stays high after ovulation, indicating that ovulation has already occurred. However, it cannot predict when ovulation will occur, and therefore, it is not an effective form of contraception.