Microcopy is the small text around an interaction: a button, field label, hint, error, empty state, or confirmation. It answers the question people have right before they hesitate.
Be specific
“Submit” gives little information. “Request a project conversation” sets a clearer expectation. A password hint can prevent an avoidable error. A form confirmation should say what happens next and when.
Write for the worried moment
Explain whether data was saved, whether payment went through, and how to recover. Avoid blaming the person for an error the interface helped create.
Good microcopy works best when the wider user experience has a clear purpose.