the.com/empty set

means The unique set that has no members at all — written ∅ or {} — and every other set is built up logically from this foundation of nothing.

from The symbol ∅ comes from Scandinavian alphabets (a letter like Norwegian/Danish Ø), introduced into mathematics by the 20th-century Bourbaki group of French mathematicians, who wanted a distinct character not to be confused with the Greek letter phi or the digit zero. The concept itself traces back to set theory's founders — Cantor and others in the late 1800s — who needed a way to talk rigorously about 'collections with nothing in them' so that operations like intersection always produce a set, even when two sets share no elements.