An introduction is a nanopublication that links a key to you: it names you, states your public key, and is signed with that very key. Nanodash creates and publishes it from your profile page when you make a key. It is the one nanopublication everything else depends on, since it is how the network learns which signatures are yours.

Each key gets its own introduction. A person with a key in Nanodash and another on their laptop has two introductions, and both keys count as them once approved.