Skip to main content
Dictionary
Store
Blog
World
Help
Advertise
Chat
System Status
Information Collection Notice
Trademark Concerns
reCAPTCHA Privacy
Terms of Service
reCAPTCHA Terms
Privacy Policy
Accessibility
Report a Bug
Data Request
Contact Us
Security
DMCA
© 1999–2026 Urban Dictionary ®
Mugs
Tees
Hoodies
Pro Customization
Create unique products with your own words and definitions
Preview
Personalize Your Design
Your Word
Your Definition
Sigma is the eighteenth letter of the Greek alphabet. Uppercase sigma (Σ) is used in Sigma Notation, also known as summation notation in mathematics. It represents the addition of a sequence, and this sequence can be derived from values given by a function, values in a set, values present in a Free-Body Diagram, etc. Lowercase sigma (σ) represents many things across all sciences. Notably, it represents the Stefan-Boltzmann constant, a constant used in the Stefan-Boltzmann law of radiation. In chemistry, sigma bonds are a type of bond characterized by overlapping p-orbitals. In quantum mechanics, sigma represents Pauli matrices. In biology, sigma receptors are poorly understood cell receptors that bond to certain stimulants like cocaine, meth, and other drugs.
Text fits
Save
Cancel