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With its Latin prefix sub-, "below", substrate obviously refers to a layer under something else. Rock may serve as the substrate for the coral in a coral reef. Tiny wafers of silicon (or another semiconductor) serve as the substrate for computer chips. Substrate may also mean subsoil—that is, the layer under the topsoil, lacking in organic matter or humus. Substrate is part of the vocabulary of various other sciences, including chemistry and biology. But although it's mostly a scientific term, writers may also use it to mean simply "foundation"—for instance, when observing that reading is the substrate on which most other learning is based.

Merriam-Webster