Advanced Encryption Standard (AES) is a widely-used symmetric key encryption algorithm that was first published by the U.S. National Institute of Standards and Technology (NIST) in 2001. AES is a block cipher, which means that it encrypts data in fixed-size blocks (usually 128-bits) at a time, rather than encrypting the data one bit or one byte at a time. The algorithm is considered to be very secure and is used in many different applications, including the protection of sensitive data, such as credit card numbers and personal identification numbers (PINs).

The AES encryption algorithm has three different key sizes: 128-bit, 192-bit, and 256-bit. The choice of key size determines the number of rounds that the algorithm will use to encrypt the data, and also affects the amount of memory required to implement the algorithm. The 128-bit key size uses 10 rounds, the 192-bit key size uses 12 rounds, and the 256-bit key size uses 14 rounds.

The AES algorithm works by applying a series of mathematical operations to the input data (known as plaintext) and the key. These operations are designed to scramble the data in such a way that it becomes unreadable to anyone who does not have the correct key. The encryption process begins with the plaintext being divided into fixed-size blocks (usually 128-bits). Each block is then processed through a series of mathematical operations, including substitution, transposition, and mixing, using the key. These operations are designed to obscure the relationship between the plaintext and the ciphertext, making it difficult to reverse the encryption process without the key.

There are three different types of AES encryption:

1. AES-128: This type of AES encryption uses a 128-bit key size and is considered a strong encryption method. It is widely used in many different applications, including the protection of sensitive data, such as credit card numbers and personal identification numbers (PINs).
2. AES-192: This type of AES encryption uses a 192-bit key size and offers a higher level of security than AES-128. It is typically used in applications that require a higher level of security, such as the protection of military and government communications.
3. AES-256: This type of AES encryption uses a 256-bit key size and is considered the most secure of the AES encryption methods. It is typically used in applications that require the highest level of security, such as the protection of highly classified information, such as nuclear launch codes.

In addition to these standard types, there are also various modes of operation to use AES in different applications such as ECB, CBC, OFB, CFB, CTR, XTS and GCM. Most of these modes are used to encrypt data that is longer than the block size of AES, which is 128 bits. This is done by dividing the data into blocks and encrypting each block separately, using the same key. The ECB mode is the simplest of these modes, but it is not considered very secure because it does not use any mechanism to protect against message repetition. The CBC, OFB, CFB, CTR and XTS modes use a mechanism called chaining to encrypt the data, which makes them more secure. GCM (Galois/Counter Mode) is authenticated encryption mode that provides not only confidentiality but also messages integrity and authenticity.

In conclusion, AES encryption is a widely-used, highly secure symmetric key encryption algorithm considered one of the most secure encryption methods available. It has three different key sizes: 128-bit, 192-bit, and 256-bit, and also various modes of operation.