Howdy! can be replied to with just a nod and a smile. It simply means Hi! in Texan - not How are you doing?. Or you might reply, Hey Y'all Doon? if you want to engage in proper Texan interactions. Replying in proper English, well pronounced, with each syllable clearly spoken, is HIGHLY discouraged.
The crest of a wave is the point of maximum positive displacement, or upward movement, away from equilibrium, or an undisturbed state. The opposite of crest is trough, which is the point of the greatest negative, downward displacement.
There are some important terms related to wave like frequency, wavelength, wave number, velocity of wave etc. Two most important parts of waves are crest and trough by which it is travelled from one part to other part. The upper part is called the crest while the lower part is called trough.