Please give me a summary of what AES-GCM is and what are its inputs and outputs.

AES-GCM is a mode of operation for symmetric-key cryptography. It stands for Galois/Counter Mode and is an authenticated block cipher that provides integrity and authenticity on top of confidentiality. It accepts as input a key K, a plaintest P and associated data AD, and it produces as output the ciphertext C and an authentication tag T.