What is the word for an annual flood in the Nile?

The annual flood of the Nile is called the Inundation.

In ancient Egypt, it was specifically known as _Akhet_ (𓈖𓏏𓐍𓏏), which was one of the three seasons of the year:

• Akhet – Inundation (flooding)
• Peret – Growing season
• Shemu – Harvest