An approximation is a version of a piece of information that doesn't describe it exactly, but is close enough to be used. An approximation may be used either when the exact piece of information is not known, or when it's too long or complicated and people need something simpler. The most common simple adjective for an approximation is "about".

For example, if you wanted to add 2.0002 and 2.0003, you can add 2 and 2, and it would be an approximation. If you are left with a balance of $78.23 you might want to say you are left with 80 dollars. In mathematics, this is written using the 👁 {\displaystyle \approx }
symbol (e.g., 👁 {\displaystyle \pi \approx 3.1416}
).^[1]

Archimedes used polygons to approximate a circle, and to calculate an approximation for 👁 {\displaystyle \pi }
as shown below:

The more sides a polygon has, the closer it is to a circle. The orange pentagons have more space between each other and the black circle than the green octagons.

• Approximation theory
• Diophantine approximation
• Estimation
• Numerical analysis

1. ↑ "Compendium of Mathematical Symbols". Math Vault. 2020-03-01. Retrieved 2020-09-19.