What is the meaning of the term "time constant" in an RL circuit ?

In a Resistor-Inductor (RL) circuit, an inductor opposes any sudden changes in current due to its self-induced electromagnetic field. When a voltage is applied, the current does not instantly reach its maximum value; instead, it rises gradually along an exponential curve. The "time constant" (denoted by the Greek letter tau) is a specific mathematical milestone in this exponential build-up. For an RL circuit, one time constant is defined as the time it takes for the current to build up to approximately 63.2% of its final maximum value. Distractors often mix up current and voltage, or use the value 36.8%. The 36.8% figure represents the remaining amount to reach the maximum (100% - 63.2%) or the value during decay, not the initial build-up phase.