What does a receiver noise floor of -174 dBm represent?

A receiver noise floor of -174 dBm is a fundamental physical limit known as the thermal noise floor. It represents the theoretical noise power in a 1 Hz bandwidth at the input of a perfect receiver at room temperature (typically defined as 290 Kelvin). This value is derived using the formula for thermal noise power (P = kTB, where k is Boltzmann's constant, T is temperature, and B is bandwidth). Converting that tiny amount of power into decibels relative to a milliwatt (dBm) results exactly in -174 dBm. Distractors that mention a noise floor being 3 dB or 6 dB above a minimum are incorrect because -174 dBm is the absolute theoretical minimum. It is also not the 'noise figure,' which is a metric that describes how much extra noise a real receiver adds compared to this perfect baseline.