Some know “sigma” as the 18th letter of the Greek alphabet but it’s also teen slang for a cool dude. According to Know Your ...

Σ Sigma (sig-mah) Τ Tau (taw) Υ Upsilon (youp-si-lon) Φ Phi (fie or fee) Χ Chi (kie) Ψ Psi (sigh) Ω Omega (o-meg-ah) ...

Here is everything we know about what it all means. Thought it was the 18th letter of the Greek alphabet? You would be wrong.