1) the top or highest point (apex)

2) the highest point e.g. the greatest distance between the Earth and a satellite (apogee)

3) a (pointed) top of a mountain; a highest point in a record or figures (peak)

4) the distance between the highest point of one wave and that of the next (wavelength)

5) the part of the sky directly overhead; the highest point (of one's fame, fortunes etc) (zenith)