A layer of ionized gas occurring between roughly 90–150 km (56–93 mi) above the ground. It reflects medium-frequency radio waves, and thus enables them to be propagated beyond the horizon.

plural of Kennelly-Heaviside layer

(geology) A stratum laid down prior to that of a saline layer (formed from encroachment by a sea)

(computing, humorous) The user.

plural of surface boundary layer

A cake consisting of seven thin layers of baked batter interlaced with seven layers of frosting.

(oceanography) A layer of the ocean lying usually 300-500 metres deep composed of dense concentrations of pelagic animal life, that moves depending on the time of day, up at night and down during the day. It sometimes appear as if it were the seabed on sonar scopes, due to the density of life in the layer.

(analytical chemistry) Alternative spelling of thin-layer chromatography

(analytical chemistry) A form of chromatography in which the solid phase is silica gel or a similar inert material supported on a glass plate.

(meteorology) The portion of the atmosphere lying next to the surface of the earth and extending up to between 50 and 100 meters.