FOSCHINI, LUIGILUIGIFOSCHINI2020-10-062020-10-062018http://hdl.handle.net/20.500.12386/27617The term "blazar" refers to a cosmic source with a relativistic jet viewed at a small angle, so that the electromagnetic emission is affected by beaming. Historically, blazars are divided into flat-spectrum radio quasars (FSRQs) and BL Lac Objects (BL Lacs). However, the recent discovery that also Seyfert galaxies (particularly Narrow-Line Seyfert 1 Galaxies, NLS1s) could host powerful relativistic jets, has set some problem of classification of jetted active galactic nuclei (AGN). I would like to review these problems and to advance one possible solution.ELETTRONICOenMultimedia10.5281/zenodo.1471637https://zenodo.org/record/1471637#.X231RZMzbeo2018agn..confE..11FFIS/05 - ASTRONOMIA E ASTROFISICAERC sectors::Physical Sciences and Engineering::PE9 Universe sciences: astro-physics/chemistry/biology; solar systems; stellar, galactic and extragalactic astronomy, planetary systems, cosmology, space science, instrumentation