Microcopy is writing that helps users navigate a software product and prevents roadblocks in the user journey. It is a smaller component of UX copy and UX writing. Form field labels, placeholder text and error messages like "Incorrect password" are examples of microcopy.
UX copy is writing on a software product interface that directs a user toward completing a specific product action or goal. It acts as the voice of a product and works to enhance the end-to-end user experience.