The designation SCR – for Silicon Controlled Rectifier – was chosen 1957 by GE and is still common in USA. Westinghouse used the designation Trinistor, and Europe combined Thyratron and Transistor to Thyristor.
The 4 layer construction is PNPN – where the first P is the Anode, the second P the Gate und the last N the Cathode.
There are also Thyristor Tetrodes / SCR Tetrodes available; here has the first N layer also a connection = Gate. So this type can be switched by 2 Gates – one with negative and the other with positive voltage.
Photo thyristors and other special versions are available, too, even in integrated circuits.