[klibertp]

I may be wrong, as it's been some time since I worked with them, but I think XPath is both its own standard, and a part of XSL at the same time. A lot of XSLT deals with selecting nodes from the source and it happens with XPath expressions.

[masklinn]

W3C standards usually depend on and leverage other standards, so XPath is its own standard, which is used by XSLT (and XQuery, and possibly a few other things).

You can't use XSLT without XPath, but you can use XPath on its own.