# Acute Angle Definition

In geometry, an **acute angle** is defined as an **angle smaller than a right angle or 90°**. In contrast, an **angle** more **significant than a straight and acute angle lies between 180 to 360°** is known as a **reflex angle**. Moreover, an acute angle can be used to measure a right angle.

However, it doesn’t imply that how much an angle is smaller than 90 degrees.

For instance, **all the angles** are formed by a triangle **where each side is less than 90 degrees** is known as an **acute angle triangle**.

For a more precise understanding, let us have an example below:

**Note:**

To know about acute triangle, you can use our Acute Triangle Definition.