A SAS data library is a collection of one or more SAS files (including SAS data sets) organized as a logical unit. Depending on your operating system, a SAS data library could reside in a directory, a file type or minidisk, or a host system data set.
A SAS data library must be associated with a temporary name or libref before it can be used in your SAS session. The SAS System automatically assigns two librefs for you: WORK, which is associated with a temporary library, and SASUSER, which is associated with a permanent library.
In SAS/LAB software, data sets are referred to by two-level names. The first level is a libref, and the second level is the actual data set name. For example, a data set called SASUSER.DENSITY is stored in the SAS data library with the libref SASUSER, and it has the name DENSITY within that library.