A shilling was a unit of currency used in 19th century Old Britain and Ireland. The slang term for a shilling was known as a "bob." A shilling was equal to twelve old pennies (1s = 12d), or one-twentieth of a pound.
During their Sherlock Holmes holoprogram, Data told Geordi La Forge about the "famous Holmes violin", telling him that it was purchased "in a pawn shop in Tottenham Court Road for fifty-five shillings." (TNG: "Elementary, Dear Data")
In the Fair Haven holoprogram, Seamus asked Tom Paris for one or two shillings because his wife had thrown him out. Later, he again asked for one or two to buy his wife a new parasol after they had come together again.
Later, Paris took bets on an arm wrestling contest between Harry Kim and Liam. Seamus bet three bob on Liam, The Doctor bet five shillings on Liam, but then placed two shillings on Kim so not to hurt his feelings. (VOY: "Fair Haven")
In a later visit to the Fair Haven program, Paris told Seamus about coming into an inheritance after his grandfather died, to which Seamus stated, "I'd drink a toast to him, if I had a shilling to me name." Later on, Milo bet Paris three shillings that he could beat him at rings. (VOY: "Spirit Folk")