This is an entry in our Disneyland 101 Glossary: Disneyland Resort definitions in under 101 words, from Mouse Brief.
Popcorn at Disneyland Resort is sold in both disposable containers and souvenir popcorn buckets. The buckets are usually not actually shaped like a bucket and instead have elaborate seasonal and other limited-time designs. For this reason, the popcorn buckets have become a popular item for collectors. You may see long lines for these buckets or spot them on resale sites for high prices.
Be sure to look out for the roastie toastie popcorn turners if you stop at a popcorn cart.