On my echocardiogram, it says "ef (teich): 72.8%". what does this mean please?

Very normal: Ejection fraction is a measurement of the strength of your heart's (actually, the left ventricle's) contraction. More precisely, it's the amount of blood ejected in a single beat. Normal is >55%. At 73%, you're very much in the normal range. (just for reference, nobody is 100%!). There are many methods of calculating EF. Teich is a commonly used standard.

Very normal: Teich is the abbreviation of Teicholz method; scientist who came up with calculation using US to estimate left ventricle ejection fraction. Any number above 55% is typically considered normal. So this basically means your main pumping chamber in the heart is functioning normally with effective forward flow.