In addition to the six variable-star types described above, certain other symbols may be found in the Type data field:BLLAC Extragalactic BL Lacertae-type objects. These are compact quasistellar objects showing almost continuous spectra with weak emission and absorption lines and relatively rapid irregular light changes with amplitudes up to 3 mag in V or more. Sources of strong X-ray radiation and radio waves, their emission displays strong and variable linear polarization in the visible and infrared spectral regions. Some objects of this type, considered erroneously to be variable stars and designated in the GCVS system, will probably sometimes be included in the main table of the Catalogue in the future, too.CST Nonvariable stars, formerly suspected to be variable and hastily designated. Further observations have not confirmed their variability.GAL Optically variable quasistellar extragalactic objects (active galactic nuclei [AGNs]) considered to be variable stars by mistake.L: Unstudied variable stars with slow light changes.QSO Optically variable quasistellar extragalactic sources (quasars) that earlier were erroneously considered to be variable stars.S: Unstudied variable stars with rapid light changes.* Unique variable stars outside the range of the classifications described above. These probably represent either short stages of transition from one variability type to another or the earliest and latest evolutionary stages of these types, or they are insufficiently studied members of future new types of variables.+ If a variable star belongs to several types of light variability simultaneously, the types are joined in the Type field by a "+" sign (e.g., E+UG, UV+BY).