Categories are unique accounts in Pockity which only support expense entries.
They are never owned by the user, and always get credited.
Reimbursements is a specialized category used by the app for reimbursement/income entries. It is the only category that supports both expenses and incomes.
Categories support Weekly and Monthly budgets.
When you setup a budget on a category, you can setup both Lock screen and Home screen widgets to get a visual representation of your expenses in such categories.
Budgets are also displayed when creating a new expense, so you always know how much you have left to spend in that specific category.
Rollover budgets are currently not supported in Pockity, however, it is planned for a near-future update following the public release of the app later this year.