OJ 287 is a bright BL Lac object, also known as a blazar. Blazars are supermassive black holes that reside at the centers of distant galaxies. As the black hole accretes matter from the galaxy, some of this material is launched into space away from the black hole as a jet of material moving at close to the speed of light. Many black holes likely emit jets during the accretion process, but blazars are relatively scarce objects because we're looking straight down the beam of the jet -- they're not so much physically unique objects as they are fortunate chance alignments with our line of sight (in much the same way that eclipsing binaries are, too -- binary stars are common, but those whose orbital plane crosses our line of sight are less common just because of random chance.) Blazars are just one of the numerous class of extragalactic sources known as Active Galactic Nuclei, or AGN.
OJ 287 has been very active recently, with AAVSO observers providing an early "heads up" to the blazar research community that this blazar is doing interesting things.