English: "Seven days" — this teaches that a sukkah that is fit to last seven days is called a sukkah, and one that is not fit to last seven days is not called a sukkah.
On the daf / in context: A structure too flimsy to stand for the full seven days does not qualify as a sukkah.
Type of Learning
Derash on the verse (Sukkah) — a sukkah must be capable of lasting seven days.
What Is Learned
A sukkah that is too unstable to stand for seven days is invalid.