Undercut
Hair clipped very short or shaved underneath or at the sides, with longer hair left on top.
Also: disconnected undercut
An undercut is a cut where the hair underneath, usually at the sides and back or at the nape, is clipped or shaved short and is not blended into the longer hair above it. The longer top can be slicked back, swept to one side or tied up. A hidden undercut at the nape thins very thick hair and can be shown when the hair is lifted into a bun. The style was common among boys in the early 20th century and returned in the 2010s.