Your recycle bin with all deleted items is at the bottom of your left-hand menu.
Everything that is deleted (tasks, events, teams and users) stays here until it's discarded forever.
In the meantime you can recover the items and they'll move back to their previous state.
If you click on a item you can recover or delete it forever.
A deleted forever item will no longer show in any record, including activity on track and plan.
You can also delete several same type items by selecting the "Delete All" option on the right of the items' list.