Tablespaces
A tablespace is a logical structure, which exists only within the context of an Oracle database. Each tablespace is composed of physical structures called datafiles; each tablespace must consist of one or more datafiles, and each datafile can belong to only one tablespace. When you create a table, you can specify the tablespace in which you want to create it. Oracle will then find space for it in one of the datafiles that make up the tablespace.
Figure 1-2 shows the relationship of tablespaces to datafiles for a database. This figure shows two tablespaces within an Oracle database. When you create a new table in this Oracle database, you may place it in the DATA1 tablespace or the DATA2 tablespace. It will physically reside in one of the datafiles that make up the specified tablespace.

Figure 1-2. Tablespaces and datafiles