A positive deflection after the ST segment which represents ventricular repolarization
Normally upright in all leads, except inverted in aVR, V1, III
Normal amplitude is < 5mm in limb leads, < 10 mm in precordial leads
Non-specific is flat or slightly inverted
Pay attention to its shape and height.
Here is a list of several different conditions where the T wave amplitude and morphology are important: