In 1977, what was labelled "Wow!"?

On 15 August 1977, a strong narrow radio signal got astronomers and extra-terrestrial hunters excited. They labeled the sound as "Wow!" The signal was intense and lasted for 72 seconds. It was not actually discovered until a few days later when reviewing the data stream. There is still no conclusive proof as to what caused the intense signal though there are a few theories that do not require it to be of an artificial construction.

https://en.wikipedia.org/wiki/Wow!_signal