The Burp function, called AquaQuake by some, allows you to vibrate the speaker of a marine VHF, to spray out any condensation.

Burp n.1

The Burp function, present on some portable marine VHF, causes the speaker to emit a very low frequency tone, which causes the speaker to vibrate, so any condensation deposited on the speaker, is sprayed out of the protection grid.

Useful in case of bad weather conditions, to remove any condensation or splashes deposited on the speaker that would otherwise degrade the audio quality output.