What's the crack? What's the craic?
Officialy: What's the craic? Craic being an Irish language word for good times/ gossip/music/ drinking/ debauchery of any kind/ or good clean fun.
Not specifically linked to crack of the crack-cocaine definition.
If asked this question by an Irish person, you are expected to give a reply which includes information on how you are, what you are doing, where are you going, with whom are you going there, have you any interesting gossip one might like to hear about, and so on. It is a question to which there are many possible answers, and it is used with great frequency on the Emerald Isle.

the word craic has many, many meanings. it can be a description of a night out that was brilliant e.g. last night was great craic. Or if you say 'we were having the craic with those girls' means that we were having a laugh and banter with those girls. one can also say 'how was the craic?' to enquire 'was it good' to which one answers 'the craic was 90' if it was good or 'it was no craic' if it was not enjoyable

The Craic (Pronounced ‘crack’) – An Irish word with no direct translation in English. Means partying, enjoying the company of others, having a good time and a fair amount more.

One elder statesman of the London Irish community advised us that "Craic" is an acronym as follows;

Ceol(Music)
Rince(Dance)
Amhrain(Songs)
Inis Scealta(Storytelling)
Cainte(Gossip)

Irish word for banter, having a good time.
Now used in colloquial English for describing a night out drinking.

irish word for "fun", "Sport".....

Craic, Having fun, having a good time, the latest info on whats happening in your social circle. Saying whats the craic? is similar to saying whats up? The word craic seems to stem from Northern Ireland slang. But has branched out due to being picked up by tourists who have exported the term.

.The craic (pron. "crack") is the feng shui of a se’siun. It is the combination of the music, the drink, the conversations, the spirit of the surroundings, and trying to make headway with people of the opposite sex. The craic is what drives all emotion and music that comes from the soul.

Irish, word for fun or a good time, can also be used in conjuction with bad to give bad craic, obviously the opposite of good craic.

Highly versatile word used throughout Ireland (not just the north as has been asserted by some) ,meaning (shared and /or convival) fun, or excitement e.g."great crack at the disco last night!", also news "What's the crack?" It also has a subsidiary meaning of "Funny business". "Don't come that crack with me!" (Don't mess with me) Clearly related to "crack" in standard English, as in "wisecracks,""cracking jokes" etc.While proponents of "Ulster-Scots" (northern Hiberno-English) claim that it was assimilated into Irish and then Hiberno-English from Scots or Ulster-Scots the truth is more complex. The (Gaelic) Irish lexicographer Dineen lists the term "cracaire" (basically an asshole!) neary a century ago while Newnes New Comprehensive Dictionary of the English Languge (circa 1920)ascribes Dutch, Anglo-Saxon and Gaelic antecedents to the word "crack" when used in the sense of fun or chat - but not in Scots (language) except in the sense of "an instant" e.g. "the crack of dawn". The spelling "craic" is of relatively recent origin, probably for pseudo-aesthetic reasons.Whatever its antecedence it is clear that the word has now evolved a uniquely Irish and largely gaelic persona.