What is a t wave abnormality on an ecg?

Buy an ECG textbook: The deflections of the lines on an ECG are given names: the P wave is atrial depolarization, the next downward deflection is the q wave, then up is the R wave and down is s, which is ventricular depol., followed by a t wave which is ventricular repol. Usually t waves go the same direction as qrs, are assymtrical and of certain amplitude. Anything other than this can be "abnorm".

Ecg: T waves represent the repolarization of the ventricles. The morphology of the wave is fairly uniform so when its vector is in the wrong direction we consider the t wave abnormal.