This spell causes magical chains to snake out of a chair and bind a person to it.
References from the canon
Charlie Weasley and the other dragonkeepers used leather and chains to control the dragons for the First Task of the Triwizard Tournament (GF19).
The chair in the Court of Magical Law has these magical chains on it (GF30, OP8). The appearance of the chair "gave Harry an ominous feeling" when he saw it in Dumbledore's Pensieve. Several Death Eaters were chained to the chairs including Igor Karkaroff, Bellatrix Lestrange, brothers Rodolphus and Rabastan Lestrange, and Barty Crouch, Jr. While Ludo Bagman was also put on trial at the same time, he was not chained and was shown more leniency, probably because he was a famous sports figure.