From web.mit.eduSAP Modules
SAP stands for Systems Applications and Products. It is the name of both an online financial and administrative software and the company that developed it. SAP is made up of individual, integrated software modules that perform various organizational system tasks. MIT has customized and implemented the SAP modules that best suit its organizational needs.
An SAP environment is a completely self-contained version of the SAP database, designated for a specific purpose. As an SAP end-user, you will be working in the Production, Practice, and Training environments.
A client is a self-contained unit in an SAP R/3 system with its own separate master records and set of tables. You don't need to remember what client to use on Production; simply accept whatever the system defaults to on startup.