Bonding is what happens when you develop a close emotional connection with another person, or when two things are fastened together. Touching your tongue to a frozen flagpole is one way of bonding, though this is not recommended.
When a baby hippo in the zoo snuggles up to her mother, bonding is happening. And though it may not seem like it, even sitting for hours in the backseat with your annoying little brother is a kind of bonding, or building a relationship through constant contact. In addition to this emotional bonding, there's a physical kind of bonding, like when you superglue a quarter to the floor to trick your little brother.