Seyfert galaxies are ordinary-looking galaxies, usually spiral, observed for the first time in 1943 by Karl Seyfert and belonging to the active galactic nucleus (AGN) class. They emit powerfully in the radio spectrum, more than radio galaxies, but also in the visible spectrum.
Examples are the NGC 1410 galaxies in the constellation of Eridan and M77 in the constellation of the Whale.
A particular feature of a Seyfert galaxy is a nucleus that is very bright in the visible spectrum. Here it is the first thing to appear on a photograph and only increasing the exposure time reveals the AGN galaxy.
An image of a Seyfert galaxy from Hubble; note the particularly bright nucleus.