Can I make a collider ignore only one other collider?

(3d project, unity c#) Lets say I have 2 types of objects, ghosts and nonghosts. I want the ghosts to be able to interact with triggers, but not things in the world. I want the nonghosts to interact with everything except for the ghosts. I have a box collider on the ghosts so that they still activate the triggers, but this means that they can interact with objects in the world. Is there an option I can change to make the ghosts ignore objects that aren’t triggers?

While you can use layers as @Bunny83 suggested, there are some circumstances where it can be difficult to use them, either because you need things to be on the same layers for other reasons, you run out of layers, or something else. In those cases you can also use Physics.IgnoreCollision ()

Sure, just use layers. So create two additional layers for your “ghosts” and “nonghosts” and go to Edit -> Project Settings -> Physics and choose which layers can collide with each other.