signal-to-noise ratio

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun The ratio of the power of an electrical, electromagnetic, or optical signal to the power of background noise accompanying the signal.
• noun The ease with which useful information can be discerned in the context of much noise, talk, or undesired information.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun sciences A figure of merit comparing the strength of a signal carrying information to the noise interfering with it.
• noun colloquial A way of describing how much interesting information is included in a message or conversation.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun the ratio of signal intensity to noise intensity