Signal-to-noise ratio is a measure that compares the level of a signal to the level of background noise, to see how strong the signal actually is. The same phrase is sometimes used to refer to the amount of useful information to false information in an online exchange–for instance, if somebody says that the signal-to-noise ratio is low on a forum or online community, they usually mean that there is a lot more spam and off-topic nonsense than actually useful posts. A ratio of high would mean a good signal, whereas low means a bad signal.