Basic interpretation of ECG

Here is a textbook-perfect segment of an ECG. What's the flat line, without any deflections, called?

What is the first upward wave called?

Sometimes there is a downward deflection at this point. What is it called?

What is the combination called of a downward deflection, followed by an upward deflection, followed by another download inflection?

The fourth step is interpreting the QRS complex (representing depolarisation of the ventricles), which has several sub-steps. First, consider the cardiac axis. The wave of depolarisation spreads in multiple directions through the ventricles. The differing magnitudes and directions of the various depolarisation currents can be “summed” to form a resulting electrical vector, which is known as the cardiac axis.

If we consider the heart in the coronal plane (using the limb leads), an abnormal axis is outside -30 to +90 degrees. What are the steps to determining the cardiac axis?

For the fifth step, consider the ST segment. ST segments can be elevated or depressed from the iso-electric line. The ST-segment is said to be depressed if it slopes down 1mm or more from the J-point, or is depressed 1mm or more horizontally. ST-segment elevation of up to 3 mm in the right-sided chest leads, and up to 1 mm in the limb leads may be normal, and is referred to as early repolarisation.

What conditions do these phenomena indicate?