Non-dualism

Not one, not two.

Typically means that you are not separate from the universe. You are a drop in the ocean, not separate from the ocean. Thinking that the universe is out there while you're in your head, separate, isolated, is the source of much duhkha.

I've also found it useful in the linguistic sense of not binary. We don't live in a binary world but language often forces us to talk as if we do. Non-dual thinking means constantly reminding yourself that the answer is may not be yes OR no, it may be yes AND no, or it might be not-yes AND not-no, or some other option that doesn't fit into the neat baskets that language forces on us.