A Field
A single piece of information is known as a value.
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A single piece of salt is called a grain or a crystal.
Galley's
A single strand of human hair is called a "strand" or "hair follicle".
A value
In draughts, a single piece cannot directly take a double piece in a single move. However, if a single piece jumps over an opponent's single piece that is adjacent to a double, it can then continue its jump over the double piece if the position allows for it. Thus, the single piece can indirectly take a double by jumping over a single piece first.
A single 'piece' of sand is called a 'grain'.
The common term for a single mosaic piece it tessera, but can also be called abaciscus or abaculus. Each piece is made of a single small tile, which is usually cube shaped. Tesseras are usually made from clay, ceramic, stone, glass, or mirror.
A coiled piece of DNA is called a plasmid, found in prokaryotic cells.
Your wife's sister is called your "sister in-law".