- AES: Advanced Encryption Standard. This is the name of the encryption algorithm (symmetric encryption). Other symmetric encryption algorithms are: DES, 3-DES etc.
- 128: This probably refers to the key size. AES encryption uses 3 key sizes (128bit, 192bit and 256bit). Block size in AES is also 128 bits.
- CBC: This is the mode of encryption that you want. There are number of modes of encryption, which depends on how fast you want your algorithm to work, parallelism and level of security. A few modes are CBC(Cipher Block Chaining), ECB(Electronic Code Book), CFB(Cipher Feed Back), CTR (Counter) etc.
Now, your client asked you to encrypt using AES-128. So, you should be using AES encryption with 128 bit key size. Any mode you can use will be of your preference. I'd prefer CBC.