BL Lacertae objects, or BL Lacs, are a type of active galactic nucleus characterized by their strong and variable emissions across the electromagnetic spectrum. They are a subclass of blazars, which are known for their jets of particles that are directed towards Earth. BL Lacs are distinguished by their featureless optical spectra and rapid brightness changes, making them unique among other astronomical objects. These objects are powered by supermassive black holes at their centers, which consume surrounding material and emit energy as a result. The jets produced can extend for thousands of light-years and are responsible for the intense radiation observed. BL Lacertae objects are important for studying the behavior of high-energy astrophysics and the evolution of galaxies.