Simply defined, a transmission is the torque-transmitting link between the engine and the wheels of your car. And, manual and automatic gearboxes are no longer the only option; many modern cars use continuously variable transmissions, but these, too, are subject to gearbox failure, even though they don't technically have gears. While we discuss the different types of transmission in-depth here, suffice it to say that since it is a hard-working component of your drivetrain, it can wear out.
Read more - Make Sure To Never Miss These Signs Of A Transmission Problem