Ask 10 Japanese to tell you exactly what a sunakku (snack) is and you'll likely get 10 different answers.

For a definitive explanation, then, the logical people to ask are those whose job it is to monitor snacks, bars and any other places that serve booze: the police. However, even they brushed aside any attempt to categorize the omnipresent snack.

"There is no definition," said an official at the National Police Agency, citing the fact that snacks come in more varieties than Pocky.

Above-board snacks all have in common that they provide light fare. Some open during the day, serving coffee, before switching to alcohol as evening draws on. Others don't open until the sun goes down.

Then there's the underworld variety. Examples include a category known to human-rights monitors as "dating snacks," spots where the "hostesses" can be hired to perform sexual services off the premises; and ostentatious, closet-size brothels in sleazy districts where prostitutes await customers in booths labeled "Snack." Many of these places, say police and activists, are simply fronts for operations often employing foreign women brought to Japan by trafficking rings. Usually they have a mama-san, too -- though a better name might be a "madam."

Whether glitzy or shady, these now commonplace snacks first appeared around 1964, the year of the Tokyo Olympics and during a period of high economic growth coupled with rising demand for leisure amenities.

Experts say the impetus behind snacks was the enactment of local regulations banning fuzoku (Japanese for "public custom," but best read as "vice") businesses -- including bars, cabarets and dancehalls -- from staying open into the wee hours. That sparked demand for places that could circumvent the new proscriptions, according to the Guidance Center for National Sei-Ei Businesses, an organization that monitors Japanese lifestyles.

Because snacks serve food in addition to drink, they managed to classify themselves as restaurants rather than bars -- and thus fit the bill. Today, it is not uncommon for a snack to stay open until 2 a.m.

Snacks wriggle through loopholes in other ways, too. No Japanese man is drawn to one solely for the drinks, which he can get cheaper and in greater variety elsewhere. Rather, he goes to be pampered by the mama-san.

The Japanese term for the brand of hospitality available at a snack is settai, which is defined in the Law Regulating Adult Entertainment Business as "entertaining a customer in a fashion that creates an environment conducive to pleasure."

Police officials interpret this to include sitting beside customers on a sofa, mixing their drinks (rather than just pouring them), lighting their cigarettes or even engaging in a karaoke duet. However, snacks need official, legal permission for settai -- and even then must cease and desist at either midnight or 1 a.m.

Of course, controlling human nature is -- as the saying goes -- like trying to herd cats, so settai does go on at even the most respectable snack bars, with or without permission, and often until well after midnight; indeed, it is their very raison d'e^tre. And only a puritan would consider settai -- as it is performed at the snack, between a middle-aged woman, her workworn client and, if he's married, occasionally even his wife -- as anything more than harmless play.

Off the record, police say that rather than pressure every little snack, they prefer to use the statutes as tools for cracking down on serious offenders, such as massage parlors employing minors.

So, for now, the common man can rest assured that come Friday night, mama-san will be there, waiting for him, with a bottle in hand and a welcoming smile on her face.