The Howdy Glossary

S3 may refer to the Simple Storage Service provided by Amazon Web Services for object storage. Data is stored in "buckets," and can be easily accessed through the internet. It is widely used for backup, archiving, big data analytics, and disaster recovery applications.
S3 also stands for "Simple Scalable Scripting", which is a cloud-based computing platform by Google designed for rapid development of web-based applications using HTML, CSS, and JavaScript.
The third possibility is that you are referring to the original object-oriented system developed with Alan Kay's Smalltalk at Xerox PARC in 1970.