SAP systems consists of more than one client - technically 1000 client can be created in one system. So we need to identify which client is the business client. Preciously SAP is client based (A mandatory field while login)
Each client is defined with a logical system name that is defined in SALE. (Sap System linking and enabling). Each system is identified by SID, client by 3 digit number. So, Logical system number should be <SID>CLNT<CLNT_Number>
To identify the systems easily by name
1. Goto > SALE > Basic Settings > Logical System
2. Define Logical System (<SID>CLNT009)
3. Assign logical system to the client.
There should be unique SID in the Landscape.
You can also get information regarding SAP BASIS