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A colon before an equals sign, marking a definition rather than a claim.
Also known as: Colon equals, Definition sign, Assignment operator, Is defined to be
A colon before the equals sign says the left-hand side is being defined to mean the right, rather than asserted to equal it. The distinction matters because a definition cannot be false, and a triangle over the equals sign or the word 'def' above it does the same job.
Marks a definition: the symbol on the left is introduced as an abbreviation for the expression on the right.
Contexts: Mathematics
Is written variously as a colon-equals, an equals sign with a small triangle above it, or an equals sign with 'def' above it, all with the same meaning.
Contexts: Mathematics
Doubles as the assignment operator in several programming languages, where it means a variable is being given a value.
Contexts: Mathematics
Two small dots one above the other followed immediately by two short parallel horizontal lines.
One asserts equality, the other creates it by fiat.