A member of the brass family of musical Instruments and one of the oldest. In its most basic form it is a length of cylindrical brass tubing bent into a compact shape with a bell at one end and a mouthpiece at the other. The sound is produced basically by amplifying and altering the pitch of a buzzing sound sound produced by blowing air through the lips held next to the mouhpiece.
Modern trumpets have valves to alter the length of the tube and produce a greater range. It is the length of pipe and the standing wave that can be produced in it that provides the fundamental note.
Trumpets are commonly tuned to Bb but others exist (C to A including Eb) and have a range of about 3 octaves. They exist from the high piccolo to the low bass.
The Cornet and Flugelhorn are similar instruments but have conical tubing rather than cylindrical and a few more bends.
It is not really a Folk instrument but is used effectively in bands fusing brass sections with traditional instruments.