Q.Explain the term “universal gates”.

A universal gate is one from which any other logic gate, and therefore any logic function, can be built using only that single type of gate. …

[!TLDR]

NAND and NOR are called universal gates because the basic AND, OR and NOT gates, and thus any logic circuit, can be made from either one of them alone.

A gate is termed universal if it is functionally complete — that is, it can implement the complete set of basic operations (AND, OR, NOT) on its own. Since every Boolean expression is ultimately a combination of these three operations, a functionally complete gate can build any digital circuit whatsoever. This has a strong practical advantage in manufacturing: a designer can stock a single type of gate IC (for example the 7400 NAND or 7402 NOR) and still realise an entire system, simplifying inventory, wiring and fabrication. …