Centered beams
Centered beams are positioned between high and low notes within the same beamed group, typically drawn in the middle of the staff or between the staves of grand staff instruments.
Centered beams are also known as kneed or elbowed beams due to their often angular shape.
When a beamed phrase spans a large pitch range, normal beams are often positioned very close to some notes in the phrase but very far from other notes in the phrase, making some stems very long. Having a centered beam in a phrase that spans a large pitch range can reduce the maximum distance between noteheads and the beam, but can also place the beam within the staff, which can obscure staff lines.