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:  While not included in Oracle Standard Edition or Oracle Standard Edition One, the latter two editions offer a subset of spatial features (called Oracle Locator) at no additional cost. The appendix to this guide details the functions supported by Oracle Locator.