Signal-to-noise ratio, formally used, applies to electricity and engineering, and refers to how much of a desired signal is being received, versus how much background noise is coming through.
The same thing applies to your database. The signal is your good data; the noise is your bad data. I've argued for years that the higher your signal-to-noise ratio in your database, the more likely you are to enter the cycle of doom, where staff will no longer trust the data, and stop using it. Bad data, including outdated contacts, is noise.
In order to improve your signal-to-noise ratio, you need to continually monitor and clean your data. Here are some ways you might do that.