The answer depends on whom you're talking to. Colloquially, the two terms are often used interchangeably, and in some types of cooking, such as classic French cuisine, there's no distinction between the two. But in North American cooking, the definitions can vary.
While beef, turkey, or chicken broth is made generally from meat, stock is produced by simmering browned vegetables and bones. As a result of the gelatin released from the bones, stock tends to have more viscosity and a fuller mouthfeel. The browning also creates a darker color and a roasted flavor.