Estimation

Estimation is the approximation of a result that one can use with information that is not clear or is incomplete. It is like making an educated, reasonable guess based on the information given.

If an estimate is more than the actual amount, then it is called an overestimate.^[1] If the estimate was less than the actual result, then it is called an underestimate.^[2] This is different from a prediction.

References

↑ James Tate, John Schoonbeck, Reviewing Mathematics (2003), page 27: "An overestimate is an estimate you know is greater than the exact answer".
↑ James Tate, John Schoonbeck, Reviewing Mathematics (2003), page 27: "An underestimate is an estimate you know is less than the exact answer".

Other websites

Estimation chapter from "Applied Software Project Management" (PDF)

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[1] James Tate, John Schoonbeck, Reviewing Mathematics (2003), page 27: "An overestimate is an estimate you know is greater than the exact answer".

[2] James Tate, John Schoonbeck, Reviewing Mathematics (2003), page 27: "An underestimate is an estimate you know is less than the exact answer".

[1]

[2]