Quick note is a Markdown scratchpad persisted and synced across all your devices for things like quick notes during meetings, checklists, reminders, etc.
Think of the quick note as one note available all the time in your sight right next to your tasks.
This screenshot is from an older version of Lunatask. The app looks different these days, but the functionality of the feature showcased here is the same.
If you are using Lunatask on multiple computers, you can use the quick note to share short text snippets or links between them.
Although the formatting toolbar is not available here, you can still use Markdown to add formatting or checklists to your quick note.