The unit for wavelength depends on the system of units being used. In the International System of Units (SI), which is commonly used in scientific contexts, the unit for wavelength is meters (m).
For example, if you are measuring the wavelength of light, you would express it in meters. So, a wavelength of 500 nanometers (nm) would be equivalent to 500 x 10^(-9) meters.
In some cases, other units such as angstroms (Å) or nanometers (nm) are also used for convenience, especially when dealing with atomic or molecular scales. An angstrom is equal to 10^(-10) meters, and a nanometer is equal to 10^(-9) meters.
It's worth noting that in different fields or specialized contexts, other units might be used. For instance, in spectroscopy, the unit of wavelength might be expressed in reciprocal centimeters (cm^(-1)) or wavenumbers.
Overall, the choice of unit for wavelength depends on the specific application and the system of units being employed.