Plain English Meaning
Slices of airspace stacked on top of each other like floors in a building. Each floor covers a certain range of heights.
Full Definition
Defined bands or layers of airspace stacked vertically, each covering a specific range of altitudes. In en route operations, airspace is organized into these layers so that traffic, navigation services, and procedures can be managed at different altitude levels.
Context Anchor
Seen in instrument en route procedure discussions, especially when substitute airway procedures or route rules change with altitude.
Derivation
From Latin stratum, meaning 'a layer' or 'something spread out.' The plural is . The word is used in geology for layers of rock, and borrows it for layers of airspace stacked by altitude.