basal body temperature
nounMedical Definition of basal body temperature
: the temperature of the body at rest that is typically taken immediately after waking from sleep
Note: The basal body temperature of a woman slightly rises during ovulation and may be tracked to estimate when future ovulation will occur.
When she ovulates, her basal body temperature rises about one degree and remains elevated until her next period.— Jane E. Brody, The New York Times, 1 Jan. 2002