What is "hoop lock"

Hoop \Hoop\, n. [OE. hope; akin to D. hoep, hoepel.]

1. A pliant strip of wood or metal bent in a circular form, and united at the ends, for holding together the staves of casks, tubs, etc.

2. A ring; a circular band; anything resembling a hoop, as the cylinder (cheese hoop) in which the curd is pressed in making cheese.

3. A circle, or combination of circles, of thin whalebone, metal, or other elastic material, used for expanding the skirts of ladies' dresses; crinoline; -- used chiefly in the plural.

   Though stiff with hoops, and armed with ribs of whale.
   --Pope.

4. A quart pot; -- so called because originally bound with hoops, like a barrel. Also, a portion of the contents measured by the distance between the hoops. [Obs.]

5. An old measure of capacity, variously estimated at from one to four pecks. [Eng.]
   --Halliwell.

   Bulge hoop, Chine hoop, Quarter hoop, the hoop nearest the middle of a cask, that nearest the end, and the intermediate hoop between these two, respectively.

   Flat hoop, a wooden hoop dressed flat on both sides.

   Half-round hoop, a wooden hoop left rounding and undressed on the outside.

   Hoop iron, iron in thin narrow strips, used for making hoops.

   Hoop lock, the fastening for uniting the ends of wooden hoops by notching and interlocking them.

   Hoop skirt, a framework of hoops for expanding the skirts of a woman's dress; -- called also hoop petticoat.

   Hoop snake (Zo["o]l.), a harmless snake of the Southern United States ( Abaster erythrogrammus); -- so called from the mistaken notion that it curves itself into a hoop, taking its tail into its mouth, and rolls along with great velocity.

   Hoop tree (Bot.), a small West Indian tree ( Melia sempervirens), of the Mahogany family.