Definitions for "Placed"
Keywords:  supremacy
situated in a particular spot or position; "valuable centrally located urban land"; "strategically placed artillery"; "a house set on a hilltop"; "nicely situated on a quiet riverbank"
put in position in relation to other things; "end tables placed conveniently"
Keywords:  fourth, horse, third, depends, comes
If a horse comes first, second, third or fourth (but not necessarily all of them, the range depends on the size of the field), the selection is said to have been 'placed'.
A placed bet means you bet on a participant, usually in horse racing, coming second, third or even fourth. The amount of places depending on the size of the event's field. Usually, second and third are considered places, and sometimes fourth as well.