In
telecommunication, a
mixer is a
nonlinear circuit or device that accepts as its
input two different frequencies and presents at its
output (a) a
signal equal in
frequency to the sum of the frequencies of the input signals, (b) a signal equal in frequency to the difference between the frequencies of the input signals, and, if they are not filtered out, (c) the original input frequencies.
Source: from Federal Standard 1037C
In beverage preperation, a mixer is a drink (usually non-alcoholic) that is mixed with another in the hope that the result is more palatable.