What does wavelength, frequency, and inverse relationship mean?

Wavelength = The Length of a wave
Frequency = How many waves pass in a second
Inverse Relationship = As one thing goes up, the other goes down
Wavelengths are a literal distance, usually measured in meters (sometimes with a prefix). The wavelength is measured from a certain spot on a wave to the next identical spot. (For example: Crest to Crest or Trough to Trough)
Frequency is the number of waves that pass a particular point in a second. The second time is key here, as it will never change; all that will change between different waves is the number of them that pass (Light has frequencies in the thousands usually but ocean waves will never even hit double digits).
The unit used is called Hertz and is commonly described as cycles per second (or wavelengths per second).
These two values have an inverse relationship following the wave speed formula:
Speed = Wavelength##*##Frequency
Since wave speed is set in stone for any particular circumstance, if wavelength were to increase, frequency would have to decrease to avoid changing the speed (the opposite applies as well).