Supraventricular tachycardia (SVT) is a general term that refers to any rapid heart rhythm originating above the ventricular

Ventricle (heart)

In the heart, a ventricle is one of two large chambers that collect and expel blood received from an atrium towards the peripheral beds within the body and lungs. The Atria primes the Pump...

 tissue. Supraventricular tachycardias can be contrasted to the potentially more dangerous ventricular tachycardia

Ventricular tachycardia

Ventricular tachycardia is a tachycardia, or fast heart rhythm, that originates in one of the ventricles of the heart...

s - rapid rhythms that originate within the ventricular

Ventricular tachycardia

Ventricular tachycardia is a tachycardia, or fast heart rhythm, that originates in one of the ventricles of the heart...

 tissue.
Although technically an SVT can be due to any supraventricular cause, the term is often used by clinicians to refer to one specific cause of SVT, namely Paroxysmal supraventricular tachycardia (PSVT) which is due to AV nodal reentrant tachycardia

AV nodal reentrant tachycardia

AV nodal reentrant tachycardia , or atrioventricular nodal reentrant tachycardia, is a type of tachycardia of the heart. It is a type of supraventricular tachycardia , meaning that it originates from a location within the heart above the bundle of His. AV nodal reentrant tachycardia is the most...

.
The term supraventricular tachycardia is often used differently in different settings.

• Theoretically, it refers to any tachycardia that is not ventricular in origin
  Ventricular tachycardia
  Ventricular tachycardia is a tachycardia, or fast heart rhythm, that originates in one of the ventricles of the heart...
  
  .