The quality factor (Q-factor) of an LCR circuit is a dimensionless parameter that describes an oscillators or resonators underdamped condition. It is defined as the ratio of the energy stored in the circuit to the energy dissipated per cycle. The Q-factor is a measure of the "goodness" or quality of a resonant circuit, and a higher value corresponds to a more narrow bandwidth, which is desirable in many applications. The Q-factor can be mathematically expressed as Q = X/R, where X is the capacitive or inductive reactance at resonance, and R is the series resistance.

A high Q resonant circuit has a narrow bandwidth as compared to a low Q resonant circuit. The Q-factor is an important characteristic of an LCR circuit, and it helps us understand the behavior and performance of the circuit. The following conditions are necessary for a high value of the Q-factor: (i) The value should be high, and (ii) the value of R should be lower.

In summary, the Q-factor is a measure of the sharpness of resonance in an LCR circuit, and it is defined as the ratio of the energy stored in the circuit to the energy dissipated per cycle. A higher Q-factor corresponds to a more narrow bandwidth, which is desirable in many applications.