A French polish is a shellac polish that produces a high gloss on wood. You will commonly see it on musical instruments like violins, boxes or sometimes on tables. You may also use it when you are doing repairs on antiques. Below I put a couple of photo examples that showcases the shine you get on the piece. Machine production generally does a bad job with French polishes, so this is a technique that you need a skilled woodworker for.
I didn’t know you could add turpentine to the shellac for more lubricity. That’s a great tip.