A phenomenon is an observable event or, quite literally, something that can be seen.
Phenomenon can also mean a "surprising development" or "unusually successful person".
Use in science & technology
In science, phenomenon stands for any event which we can sense or detect or record. In science, the word "observe" means more than just "visible to the naked eye". It means "sensible", available to our senses. The senses we are born with are extended by a whole range of instruments which record things we cannot see, and make them visible to us.
So, while some events are easy to observe, others need technology to make observation possible.
Phenomenon Facts for Kids. Kiddle Encyclopedia.