They're similar, lists of tasks/items to check off. However, when most people talk about checklists they're often talking about it in particular contexts and a more deliberate construct than todo lists. Pilots, for instance, have pre-flight checklists. This is not an ad hoc todo list (the more common sense of "todo list") with arbitrary and possibly unrelated tasks (go to grocery store, pick up dry cleaning, outline paper).

Checklists, especially in system operations and safety contexts, also tend to have a bit of a procedural characteristic, possibly including conditional and even looping constructs or sub-procedures.

  - If HPA is energized
    - [ ] De-energize HPA
  - [ ] Enter radome

And order is important to many, but not all, checklists in a way that's not as clear in todo lists. You can probably pick up the dry cleaning before the groceries, or on a separate errand run, for instance. If you don't de-energize the HPA, you're possibly setting yourself up for some pain and suffering if you enter the radome while the system is energized.

A todo list is a unique thing, it’s about remembering to do all the things you said you’d do. There’s no implied consistency from one todo list to another.

A checklist is used repeatedly, and it’s about completing a task (or set of tasks) to a certain standard. If you’re following a checklist, you’re aiming for consistency.

The semantics of list types is an underrated problem that probably holds back the market of software tutorials.

A todo list is typically a set of unrelated things to be performed once and annotated as "done." Something may be performed periodically, like iOS reminders adds take out the garbage on a weekly basis, but each performance is really its own item. Sometimes a todo list will have parent-child tasks.

A checklist is a two lists: one a template and the other the record of performing the checklist. The template and performance instance records are a set of related things which may or may not be ordered or conditional. A special type of checklist is an inspection checklist which may include results from performing a particular checklist item as well as the fact that it was performed.

Checklists are usually for repeatable activities (or at least similar-enough ones).

I think there are two differences: urgency and immediacy. A checklist is urgent in a way a to-do list isn't. The sky will fall if a checklist is not followed when X happens, whereas a to-do list is kind of a nebulous list of nondescript tasks. A checklist's immediacy also implies a strict ordering, whereas a to-do list does not. For example, task A must be completed before task B or the sky will fall.

It's just a lot stricter operationally, which is why I think you'd get a lot of pushback trying to implement one for non-critical business tasks.

A checklist usually have dependencies; some items should be done in specific order