Signal-to-noise ratio expresses how small the noise is relative to the signal. The higher the value, the less the sound you want tends to be buried in noise.
The basic idea
It is not only about choosing gear, since an appropriate input level and a quiet recording space improve it too.
Before you use it
When recording, capture at a sensible level with some headroom so that you do not have to raise a too-quiet signal excessively afterwards.
The noise floor is the background noise itself, while signal-to-noise ratio is the measure of its relationship to the signal.
