The approximate value of something is an estimate.
An estimate is an educated guess. Approximate and round off mean "about".
guess
If an estimation, or estimate, is a guess, an approximate estimation is a rougher guess.
about, guess
Estimate
It is an estimate
Estimates are never exact. They are a best guess at what the answer is. They are always going to be approximate.
Make a very approximate estimate.
The 2010 estimate is 1,180,166,000
It's pretty much like an estimate.
An estimate is an approximate calculation of the value, number, quantity, or extent of something based on available information. It is not an exact measurement but rather a rough approximation.