Those are very basic English words.
1) Learn the English language.
2) Look at the definition of the words in a dictionary.
3) Look at the words in Google.
the dependence on signal frequency of the output–input ratio of an amplifier or other device.
Signal-to-noise ratio (abbreviated SNR or S/N) is a measure used in science and engineering that compares the level of a desired signal to the level of background noise. It is defined as the ratio of signal power to the noise power, often expressed in decibels.