Here's how it works:
* "To be done" implies a task or activity that needs to be completed.
* "Done" is used as a shorter, more casual way of saying "to be done".
Example:
* Formal: "The work needs to be done by Friday."
* Informal: "The work is done by Friday."
In the informal example, "done" is a shorthand for "to be done". It's understood that the work needs to be completed by Friday.
While this usage is widely accepted, it's important to be aware of the context. In formal writing or situations, using "done" in place of "to be done" might be considered grammatically incorrect.