"Come on" or "let's go". It can varyingly express impatience, encouragement, or excitement depending on its tone and context. It can also be used when parting or leaving a gathering to mean something along the lines of "alright[, goodbye]".

It originates in a contraction of ya Allah ("ya" being a vocative particle, like English "O"), although it's almost always spelled as يلا rather than يالله. It isn't related at all to the Greek verb έλα meaning "come!", not least because of how different their pronunciations are.

The term's been borrowed into a number of languages whose speakers are in close proximity to Arab countries, including but not limited to Urdu, Farsi/Persian, Hebrew, and Turkish.

A word to call someone, mainly used for foreigners.