Vocoder

[Ernesto]

A vocoder is a sound effect that can make a human voice sound synthetic. It is often used to speak like a robot, with a metallic and [monotonous] voice.
To put it simple: whenever you speak, your voice consists of two components. The first component is your basic voice type, produced by your vocal chords. It varies in pitch but remains nearly constant in type and is quite unique. Thats why you can distinguish between persons when you hear their voices. The second component is how you [modulate] the basic voice. [Modulation] means that you dynamically [amplify] and attenuate frequencies. This is done by the mouth and tongue when you speak.
The benefit of doing this is, you can make the carrier speak or sing. As a side effect, the formants voice type is absolutely irrelevant to the output so everybody (even those with an ugly voice) can create cool and futuristic samples.
If you want to hear good examples of its usage, listen to a few songs from [Zapp]

[Hina Muqadas]

A synthesizer that produces sounds from an analysis of speech input.

[Oralee]

n. Synthesized [voice] used in any [form] of [music].