So that's what it means. From Madeleine Kamman's When French Women Cook.
You use a vegetable peeler to strip away the unpleasant string of the green bean. It exposes the seeds inside. This is why, in pictures on bags of frozen green beans, and in pictures in old cookbooks, properly prepared beans look as though they have those strange oval-shaped holes along their sides. Who knew.
Drop them in boiling water, and boil vigorously, uncovered, for 6 minutes. Madeleine Kamman says that, too. Perhaps a minute more if they are quite thick, but you will want them thin and in season anyway, in late spring and summer. (I will take oath that truckloads of them are being put in cryogenic storage right now, to be brought out looking remarkably good, but a tad chewy in the mouth, at Thanksgiving. Otherwise no bean in its right mind should appear fresh and piled high in supermarket bins in late November.)
Drench them in butter, a squirt of lemon juice, and plenty of salt. They will accompany anything. Their own perfect vinous accompaniment -- a sauvignon blanc from New Zealand, surely?