My web search turns up accounts of it being Southern, Black American or/and Aussie slang. Would like some clarification on this.
From a wiki, I believe this is the definition and origin of “crack,” you seek:
"Craic" (/kræk/ KRAK) or "crack" is a term for news, gossip, fun, entertainment, and enjoyable conversation, particularly prominent in Ireland. It is often used with the definite article – the craic – as in the expression "What's the craic?" (meaning "How are you?" or "What's happening?"). The word has an unusual history; the Scots and English crack was borrowed into Irish as craic in the mid-20th century and the Irish spelling was then reborrowed into English. Under either spelling, the term has great cultural currency and significance in Ireland.