Syntax of a SAS file name
A two-level name, actually

SAS-file-name (member type DATA) A SAS file that holds data has a two-level name: libref.fileref Notice the period (.) separating the two references. The default libref is WORK. A user-defined libref points to a directory defined by the LIBNAME statement. The fileref is any valid SAS name identifying a data set.

A SAS data library on directory based systems is a directory.
A SAS data set on directory based systems is an individual file.
The WORK library is automatically defined whenever SAS runs to be a temporary directory that will be erased when the SAS session terminates.
The definition of a "temporary SAS data set" is a data set in the WORK library.