This is an entry in our Disneyland 101 Glossary: Disneyland Resort definitions in under 101 words, from Mouse Brief.
Disneyland Resort occasionally offers ticketed after-hours events. Oogie Boogie Bash is a popular example of these, and Disneyland also offers non-holiday themed Disneyland After Dark events with themes including Sweethearts Nite, Disney Channel Nite, Pride Nite and Star Wars Nite. There is usually theme-specific entertainment, merchandise and food, and guests have access to select attractions and character interactions. Tickets are open to the general public. These tickets are separate from a daily general admission ticket or Magic Keys but do usually allow guests to arrive a few hours before official park closing and the party beginning.