What does the principle of "three unifications" mean in drama creation?

In practice, the creation is based on ancient Greek and Roman literature. Boileau's "The Art of Poetry" is an important classical theoretical work, which concentrates many classical creative theories, such as the principle of "three unifications" in drama creation, which requires a single time, place and plot, that is, a play only performs one thing, and the plot must take place in the same place within one day and night. This is actually a misinterpretation of Aristotle's "three unifications".