I's a electronic component that act like a controlled diode. It can be used as a switch on some applications, but with some limits. 1- A SCR is a diode, and as such, it only conduct in one direction. 2-The SCR only turn off when the current passing it reaches zero.
Essentially an Scr is a solid state switch that will only allow current to flow in one direction. A triac is essentially two scr's in Anti- parallel that allows current to pass in both directions.
And SCR will conduct appreciable current when it is gated "on" and thus "told" to conduct. A silicon controlled rectifier(SCR) is an electronically controlled DC switch, and the gate is the terminal to which the control voltage is applied. Use the link below to learn more.
If it is a physical switch, this is called a "relay" or a "contactor". If it is a semiconductor device, it is typically a triac, SCR or a thyristor.
because it is gcr not scr
An SCS has an additional gate - the anode gate. It is physically smaller than an SCR and has smaller leakage and holding currents than an SCR.