Southern version of hi--this is actually much more common than saying yawl. Can be substituted for good morning, good afternoon, good evening, hello, hi, hiya, etc..
Typically used all by itself in a greeting and in return. Pronounced as almost having 2 syllables by extending the length of the word as it is sounded out. The 1st person says it with a higher tone of voice, while the replier says it a little lower.