Y: Used to indicate the luminance signal.
Yagi: A directional aerial array invented by Hidetsugu Yagi, a Japanese physicist. It is the form used by the majority of UHF television reception aerials, comprising a dipole connected to the aerial lead, a rear reflector and several directors in front of the dipole whose spacing sets the gain/directivity of the aerial across its designed frequency range.
Y-axis: In a graph or oscilloscope, the vertical axis of the display.
Y/C: Separate analogue luminance Y and chroma C signals which are recorded on some videotape recording formats. Also the name for the connector carrying the two signals.