It is not included in Oracle Standard Edition or Oracle Standard Edition One. However, the latter two editions allow the use of a subset of spatial features (called Oracle Locator) at no extra cost. An appendix of the Oracle Spatial and Graph Developer's Guide specifies the functions allowed in Locator.
Oracle Spatial and Graph Developer's Guide:  The inclusion of Oracle Locator is dependent on the edition of Oracle Standard Edition or Oracle Standard Edition One, but it is available for use without extra cost. The appendix provides a list of functions that are supported by Oracle Locator.