Anything that's packed is either tightly compressed or extremely crowded, like the packed auditorium during your school's annual talent show.
Use this adjective for things that are squeezed or pressed together, like a packed snowball or a packed cup of brown sugar. It's also useful for talking about overcrowded spaces of any kind, from a packed house at your band's show to a packed calendar that leaves you no time to catch up on your favorite TV show. A packed suitcase, on the other hand, is ready to go but not necessarily overstuffed.