That is a typical European folding trigger pocket pistol of a type made from c. 1880 to after WWI. That one was made after 1906, since it is in 6.35mm Browning, called .25 ACP in the U.S., a cartridge that didn't exist until that date when Fabrique Nationale in Liege introduced Browning's Model 1906 self-loading pistol in that caliber. It was made in Belgium as evidenced by the Liege proof marks.
Usually those revolvers are seen in bad shape and rarely bring more than $100 if that much on the retail market. But that one appears quite nice and has both tasteful engraving and gold inlay. If it is fully functional, and unless there are problems I don't see, I would estimate a value of about $400 retail.