TO most of us, a party is a gathering of people for food, drink and friendly conversation.

But when it comes to pickin' parties, that definition is not a perfect fit. Here the snacks are the simplest and drinks (and drinking) are light. At a pickin' party, people talk to each other with their musical instruments--sort of let their fingers do the talking.

That's because folks go to these parties for one reason--to play the bluegrass music that this area is known for.

And because there's something about the music that seems to invite--almost demand--participation (rather than just listening), its growth here has given rise to a special kind of meeting for its followers.

It will start just about the way other parties do, with greetings and catching up on what's happened since last time. But this small talk is clearly a prelude to the real business of the get-together, homemade music. As soon as three or four people have arrived (and this may be well before the announced hour, because bluegrass people have never really gotten into being fashionably late), they leave off the conversation, pop open their cases and begin tuning up. The instant they're satisfied, someone will break into a song, the others will fall in and the pickin' party is off and running.

Often an entire hour--sometimes two--will pass with little or nothing being said between songs except the "call." This consists of a few words giving the title of the next song, the key it's to be played in and maybe a thought about who'll take the lead. "How about 'Bluebird Singing' in D?" or "Let's let that fiddle player give us a little bit of 'Orange Blossom Special.' "

At some pickin' parties, everything will be loose and easy, with anybody who feels like it calling the next song (or maybe just starting in to pick a new song as soon as one ends). Then again, some people like to structure things (bureaucrats do play bluegrass), so some sessions will be fairly well organized, maybe just a bit overorganized. If the host is control-minded, the responsibility for calling the next song may stay with him. Or he may ask that people take turns calling the song, letting the job rotate clockwise, like the deal in poker. And sometimes the person who calls the song will also be in charge of it--will "manage" the song, deciding what the key will be, which instruments will lead and in what order.

Like any gathering of people with a strong common interest, a pickin' party has its own customs. For example, one musician may pay a high compliment to another by "splitting a break"--playing only half an allotted solo, then passing the lead with a nod toward the person chosen to share it. And because almost every party will have a new combination of pickers, the regulars have signals to keep things together. These can be a big help on a song like "Wildwood Flower," which has a clean and simple melody that seems natural for passing around until everybody who wants to has had a turn at it. Trouble is, it can be hard to get everybody stopped at the same time on an open-ended song like this. So the pickers use a foot signal. The person who started the song simply places one foot forward to let everybody know that the melody is being played the last time through.

If the foot is kicked backward instead, the players know that the song will end with a "turnaround," a repetition of the last few words as a tag ending.

Of course, there can be party pests (who want to call all the songs, or take the lead too often, or who won't or can't tune), and there are the instrumental introverts and extroverts, and the musical snob who wants to play only "pure" bluegrass. But these are the exception.

Pickin' parties I've known have not been restricted to those who had "made it" in any sense in bluegrass. There are always lots of guests (especially youngsters) who have the talent to play with the established pickers, and need only the opportunity.

That's one of the functions of almost all pickin' parties--to give people a chance to learn by listening to, and playing along with, others who have different skills and different styles. But the biggest reason people go to pickin' parties is simply to keep on playing bluegrass music--to take pleasure from taking part.