Where do I put code that doesn't relate to a particular object?

Questions & Answers
1

I want to have some code executed every frame, but it doesn’t relate to any one object. Is there a global update() method or something?

2

Update gets called on Components only. Just make an empty object and put your script on that. If you didn’t need the Update function, you could derive from ScriptableObject, but if you need it to Update you’ll have to put it somewhere that Unity will know to call.

3

I just made a script not tied to any object, that I could call from another object when appropriate.