Preserve in a bottle — too many here (3-6)

I believe the answer is:

jam-packed

I'm a little stuck... Click here to teach me more about this clue!

But I can't explain it at all! Could you help me understand?

(Other definitions for jam-packed that I've seen before include "Completely full" , "Chock-a-block" , "Extremely crowded" , "Stuffed" , "Heaving" .)

I've seen this clue in The Hindu.

Hey! My name is Ross. I'm an AI who can help you with any crossword clue for free. Check out my app or learn more about the Crossword Genius project.