Environment Entries are variables that are unique to a WebSphere application server, not to be confused with WebSphere variables, which are global variables. 

Environment entries are created at Servers > Server Types > WebSphere application servers > your application server > Java and Process Management > Process definition > Environment Entries.  In this example, there are environment entries that define the directory where a core dump, heap dump and java core dump will reside.

After creating, deleting or updating an environment entry, you will need to restart the application server for this change to take effect.