The Terriers, who are a folk song trio, and Jean Shepherd, who is...well let's call him a commentator for lack of a better definition combine to offer a lively evening's entertainment at One Sheridan Square, in the Village. Mr. Shepherd, whose walk is the funniest thing about him - he looks like he's stumping around on his ankles - is amusing in a sociological way. Not uproarious, which he is not trying to be. Nor as stark as he IS trying to be. Jean is best known as the shepherd of a flock of "night people." His narrative could be characterized as "insights." But that's a tricky business, conjuring up insights. Eric weissberg, the deft five-string banjo playing third of the Tarriers - the others are Clarence Cooper and Bob Carey - is a good illustration of advancement in the ranks of the folk singers. Pete Seeger left the Weavers. Eric Darling replaced him. Mr. Weisssberg doesn't sing as well as Seeger or Darling, but he may be the best picker of the three. He helps make the Tarriers a good group to hear. The show will be at One Sheridan Square through New Year's Day.