Here's why:

* Dissolves in water to release hydroxide ions (OH-): This is the defining characteristic of a base.

* High pH: Solutions of sodium hydroxide have a very high pH, typically above 12, indicating a strong base.

* Reacts readily with acids: Sodium hydroxide reacts vigorously with acids to form salt and water.

Sodium hydroxide is also commonly known as caustic soda or lye. It's a highly corrosive substance and should be handled with extreme care.