in practice

Actually, in fact, especially as opposed to theoretically or in principle. For example, In practice this contraption seems to work, although no one knows how or why. [Second half of 1500s] Also see put into practice.

In the exercise of a particular profession, as in She’s an obstetrician and has been in practice for at least ten years. [c. 1700]

In a state of being exercised so as to maintain one’s skill, as in This trumpeter is always in practice. [Early 1600s] For an antonym, see out of practice.