AWS S3 supports both Server Side Encryption and Client Side Encryption for your data at rest or stored data at disk.

In Server Side Encryption, when you upload an object, S3 encrypts it before storing into the disk and decrypts it before you access/download your data.

In Client Side Encryption, you need to encrypt your data before sending it to AWS S3 and you are responsible for decrypting it after to retrieve it from S3.