• Some pages are really heavy, full of words they don't need. When you ask for a page we give you only the words your machine needs, not all the rest.
• Pages say "go get this other thing," but that's slow, why do that? So we put the other thing in the page and send you both of them together.
• Most pages have pictures, but they're heavy pictures. We replace them with light pictures that look the same but arrive faster.
• Your machine remembers things you've looked at but not for very long. We give each thing a name that changes when the thing changes so your machine may remember it until its head is full.

(Inspired indirectly by xkcd's up goer five and proximately by people at work trying to explain our technical infrastructure in the same way. I used this word list.)