the.com/layer

means A distinct level or thickness of material (or abstraction) stacked with others to build something bigger — like paint coats, cake tiers, or software modules.

from From Middle English 'leyer,' meaning 'one who lays' — it started as a job description (someone who lays eggs, or lays bricks) before drifting, by the 1600s, into naming the thing itself that gets laid down. It's a cousin of 'lay' and 'lie,' tracing back to Old English 'lecgan,' meaning to place or set down. The sense of 'one level in a stack' is the word's job title quietly becoming its product.