Approximation Definition
An approximation is defined as having no exact figure but close enough to be used in mathematics. You can approximate a rounding number, for instance, if a value is 2.91, it can be rounded to the approximated value of 3.
For a more precise understanding of a concept, let us have some examples below:

The approximation value of Pi is 3.14, whereas the actual value is 3.14159.

If an egg took 14 minutes and 20 seconds to boil, then the approximated time take by an egg is 15 minutes.
Note:
To know about ante meridiem, you can use our Ante Meridiem Definition.