In jargon, a preface to any comment that indicates that the comment is only approximately true. The remark “To a first approximation, I feel good” might indicate that deeper questioning would reveal that not all is perfect (e.g., a nagging cough still remains after an illness).

What does it mean to make an approximation?

An approximation is a rough estimate or guess at something. When you write a budget for the month, you're making an approximation of how much you're going to spend. You can't be certain of the exact amount.

Where do we use approximation?

In science, approximation can refer to using a simpler process or model when the correct model is difficult to use. An approximate model is used to make calculations easier. Approximations might also be used if incomplete information prevents use of exact representations.