Bit depth
The number of bits used for each audio sample — and therefore how far down the noise floor sits.
Every extra bit buys roughly 6 dB of dynamic range. Sixteen bits, as on CD, gives about 96 dB; 24 bits gives a theoretical 144 dB, which no analogue circuit on Earth can deliver — in practice the mic preamp caps things around 120 dB. The point of 24-bit is generous headroom while recording, not that anyone can hear it on headphones.
Inside a DAW the maths is usually 32-bit floating point, where a signal can sail well past 0 dBFS without clipping as long as it is pulled back down before leaving the program. When the result is cut down to 16 bits for release, dither is added so the rounding error becomes smooth noise instead of audible distortion.