Dolphin intelligence refers to a dolphin's brain ability to process information and solve problems to ensure survival. Dolphins have large brains similar in size to humans and second in complexity among animals. They exhibit intelligent behaviors like self-recognition, various forms of communication using vocal, visual and tactile signals, and social abilities like being playful with humans. Some remarkable dolphin facts include that they evolved from land animals, can stay awake for weeks, teach their young to use tools, and form friendships through shared interests.