ST segment is the flat section of the ECG between end of S and start of the T wave between ventricular depolarization and repolarization EKG
Narrow and broad/Wide QRS complex morphology Low/high voltage QRS, differential diagnosis, causes and spot diagnosis on LITFL ECG library
The J point is the the junction between the termination of the QRS complex and the beginning of the ST segment. EKG J-point
QT interval is the time from the start of the Q wave to the end of the T wave, time taken for ventricular depolarisation and repolarisation
ECG PR segment is the flat, usually isoelectric segment between end of the P wave and the start of the QRS complex.