Part I, Definition 2 of Spinoza's Ethics:
A thing is called finite after its kind, when it can be limited by another thing of the same nature; for instance, a body is called finite because we always conceive another greater body. So, also, a thought is limited by another thought, but a body is not limited by thought, nor a thought by body.
This is one of the most important definitions in the book, because it's the basis of God as infinite. However, I think the definition is not fully developed here.
The universe, for example, should be limited by another universe by this definition. However, since we can only describe one universe, it's not possible to conceive another universe. I think I understand Spinoza's intention here, but, finitude in philosophical sense is much harder to describe.
The limits of an event, for example, cannot be described with this definition. An event is finite if it's bounded by a greater event. Ali has come and opened the door, then entered the house. What's the event here, Ali's arrival, his arrival and his act to open to door, his arrival and entrance to the house? How can we limit it? The limits we impose are arbitrary.We can opt to select Ali's being, from birth to death as a single event and all acts as episodes of that event.
The event problem is important, because, God is mostly an event not a thing. When you describe infinitude with the inverse of being finite, thus limitless, that we can readily assert that God event cannot be limited by another event, thus it's actually a no event. He's so perfect of an event, that it's impossible for him to stop and create a finite universe/world/human being.
I'll try to write on this book as I read further, but Spinoza's God seems to be a skeleton of definitions without much content to wrap. He's the most infinite but as it becomes a notion of superlative attributes, he's also becoming some distant being without much to give us.