What is a wavelength?

Answer 1

Wavelength is the distance between two adjacent crests in a wave front (or, correspondingly, two adjacent troughs). Easiest way to see this by tossing a rock into a still pond. The physical distance between the high points of two waves next to each other is the wavelength.

A similar concept is the frequency. The frequency is the number crests that will pass through a plane in a given length of time, like a second. Toss that same rock and you might notice a leaf bob up and down. It doesn't go anywhere, it just moves up and down as the waves pass through. The frequency is the number of times the leaf goes up and down in one second.

Mathematically, the wavelength is 1/frequency. Both are extremely useful. The frequency (or wavelength) in sound determines pitch, which gives us sound, music, etc. Since light and all electromagnetic energy is a wave (mostly), different colors are nothing more than EM energy at different wavelengths within the visible spectrum.

Answer 2

Sound and electromagnetic energy are transmitted in waves. Like waves in the ocean or ripples in a pond or bucket of water when a pebble is dropped in, the distance between two consecutive troughs or peaks in those waves is called its wavelength.

Answer 3

the wavelength of a wave is the distance between two points with equal phase,
for example two max or two min points
if L is the waveleght, f is the frequency (number of peaks passing a point in a given time) and v is the progagation speed

L = v/f

Answer 4

The length of a wave.

lamda(wavelength) = speed of the wave/nu(frequency)