Simple system flute most commonly refers to the type of flute manufactured and favored by classical European musicians during the Classical era.
Subsequently, many simple system flutes were integrated into folk music (including Irish folk music and Cuban charanga bands).
The simple system flute had a cylindrical head joint and a reverse tapered body.
The six main tone holes were heavily undercut[clarification needed] to produce even intonation and registration while providing even finger spacing.
The presence of keys (as found on the Classical flutes described above) does not preclude categorization as a "simple system" flute, as long as the primary tone holes are not keyed.