Union sign

A rounded U shape, denoting everything in either of two sets.

Also known as: Cup, U shape

MathematicalScientificStandard profile

Meanings

∪ denotes the union of two sets: everything that belongs to at least one of them. It is easily reversed with the intersection sign, which is the same shape upside down.

Officially standardisedVerified fact
Is encoded as U+222A UNION in the Mathematical Operators block.
Contexts: Mathematics
Common modern usageVerified fact
Denotes the set of everything belonging to at least one of the two sets it joins.
Contexts: Mathematics
Common modern usageVerified fact
Is read aloud as 'cup', a name that distinguishes it from the letter U and from the intersection sign read as 'cap'.
Contexts: Mathematics

Visual description

A single stroke descending, curving along the bottom and rising again, forming an open-topped rounded U with arms of equal height.

Symmetry: vertical
Orientation: upright

Commonly confused with: Intersection sign
The same shape inverted; which way up it sits is the whole distinction.
Opposite of: Intersection sign
Everything in either set, against everything in both.

Compare: Intersection (∩) vs union (∪) →

Confidence

IdentityHigh confidence: High confidence because the identity is defined by a current official standard, but multiple independent sources agree.
Historical originModerate confidence: Moderate confidence because the historical origin is documented in encyclopedic references, but multiple independent sources agree, but early or supporting evidence is limited, but the regional or cultural match to this specific claim is not precise.
Current useHigh confidence: High confidence because the current use is defined by a current official standard, but multiple independent sources agree.
Visual matchHigh confidence: High confidence because the visual match is documented in encyclopedic references, but multiple independent sources agree.

Sources

Glossary of mathematical symbols
Wikipedia · retrieved 2026-07-31
Tertiary reference. Used for what the notation means in ordinary mathematical practice and for attribution of its introduction, not for a claim that any body defines it.
Set (mathematics)
Wikipedia · retrieved 2026-07-31
Tertiary reference. Used for what the notation means in ordinary mathematical practice and for attribution of its introduction, not for a claim that any body defines it.
Unicode Code Chart: Mathematical Operators (U+2200–U+22FF)
The Unicode Consortium · retrieved 2026-07-30
Authoritative for the character's code point, name and block only. Unicode assigns identity; it does not define what a symbol means in use.

Last reviewed 2026-08-01

Part of

Set theory and logic notation

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Meanings

∪ denotes the union of two sets: everything that belongs to at least one of them. It is easily reversed with the intersection sign, which is the same shape upside down.

Officially standardisedVerified fact

Is encoded as U+222A UNION in the Mathematical Operators block.

Contexts: Mathematics

Common modern usageVerified fact

Denotes the set of everything belonging to at least one of the two sets it joins.

Contexts: Mathematics

Common modern usageVerified fact

Is read aloud as 'cup', a name that distinguishes it from the letter U and from the intersection sign read as 'cap'.

Contexts: Mathematics

Confidence

IdentityHigh confidence: High confidence because the identity is defined by a current official standard, but multiple independent sources agree.
Historical originModerate confidence: Moderate confidence because the historical origin is documented in encyclopedic references, but multiple independent sources agree, but early or supporting evidence is limited, but the regional or cultural match to this specific claim is not precise.
Current useHigh confidence: High confidence because the current use is defined by a current official standard, but multiple independent sources agree.
Visual matchHigh confidence: High confidence because the visual match is documented in encyclopedic references, but multiple independent sources agree.

Sources

Glossary of mathematical symbols
Wikipedia · retrieved 2026-07-31
Tertiary reference. Used for what the notation means in ordinary mathematical practice and for attribution of its introduction, not for a claim that any body defines it.
Set (mathematics)
Wikipedia · retrieved 2026-07-31
Tertiary reference. Used for what the notation means in ordinary mathematical practice and for attribution of its introduction, not for a claim that any body defines it.
Unicode Code Chart: Mathematical Operators (U+2200–U+22FF)
The Unicode Consortium · retrieved 2026-07-30
Authoritative for the character's code point, name and block only. Unicode assigns identity; it does not define what a symbol means in use.

Last reviewed 2026-08-01

Meanings

Visual description

Related & commonly confused symbols

Meanings

Visual description

Related & commonly confused symbols