The amplification factor, also called gain, is the extent to which an analog amplifier boosts the strength of a signal. Amplification factors are usually expressed in terms of power. The decibel (dB), a logarithmic unit, is the most common way of quantifying the gain of an amplifier.
In general an amplification factor is the numerical multiplicative factor by which some quantity is increased.
In electronics the amplification factor, or gain, is the ratio of output to input in an amplifier. In vacuum-tube theory the amplification factor (μ) of a triode has a more specific meaning: it is the ratio of the change in plate voltage to the change in control-grid voltage required to produce the same change in plate current. This parameter is commonly determined from families of plate-current characteristic curves as described in Vacuum tube characteristics.