Definition of yas in US English:

yas

(also yass, yaass)

exclamation

informal
  • Expressing great pleasure or excitement.

    ‘Yas! Now this is truly punk rock!’
    ‘free wine and cheese and candy, yass’

Origin

Mid 19th century (originally in representations of a regional pronunciation of ‘yes’): representing an informal or exaggerated pronunciation of yes.

Pronunciation