Photosystem II & I: These are protein complexes involved in photosynthesis that participate in the primary photochemistry of photosynthesis - they capture photons and transfer electrons. They're like specific spots on our sponge that do most of absorbing work.
Lumen: The interior space enclosed by thylakoid membrane; this is where protons accumulate during light-dependent reactions - think about it as absorbed water in our sponge analogy.
Cytochrome complex: A group of proteins that act as an electron carrier during photosynthesis, like a bucket brigade passing the electrons along.