My understanding is that the term "old time" is as Russ suggested and has been used as a market classification term and applied to a wide variety of musics. But I think the term Old-Timey is used by musicologists and other academics to denote a particular genre or Applachian string music usually, but not necessarily, ensemble in nature. The term old-timey is rlatively recent and wouldn't have been used by the original players it describes.

Charlie Poole would be considered old-timey and I think Clarence Ashley would be as well but the Carter Family would not be.

In old-timey music the heavy rhythm is usually squared off to meet the demands of American "hoedown" folk dancing. It has a different feel than Irish or Scottish fiddlers would employ. The five-string banjo is generally played using a clawhammer or drop-thumb technique that reinforces the fundamental rhythm. The basic rhythm might be described in text as dah da-da dah da-da dah da-da, ad infinitum. The guitar, if present, plays a continuously moving series of bass notes often with very little chord. Old-timey bands might include a Jews harp but probably wouldn't include a double bass. A mandolin might be present but it wouldn't be as prominant or as artfully played as is common is bluegrass music.

Modern old-timey players tend to have all the instruments playing the same melody at the same time in unison and they do that until everyone is tired. This wasn't always the practice with the original old-timey bands but seems to be common today.

      - Mark