What is reading? That depends on what book is being read.
Reading a mystery is like being a detective, searching for clues. Reading a thriller is like sitting on the edge of your seat waiting for the other shoe to drop. Reading a fantasy is like running through the woods, taking deep breaths of crisp, fresh air, searching for what's just out of reach. Reading science fiction is like looking at the stars, thinking what is beyond. Reading a romance is like falling in love. Reading non-fiction is like having any and all the world's knowledge right in front of you, waiting to be discovered.
Reading it's countless different things to countless different people. That's why I love it.