A Second Level page can be termed as a Child page of a First Level page.  Thus, the First Level page is the Parent page of the Child Page.  Additionally, a second Child page under the same First Level, is termed as a Sibling page.

 In this example, Online Services is the Parent page of this page:  2nd Level Page and this page, 2nd Level Page, is a child page of Online Services.

Part 2 is a Sibling page of this page, 2nd Level Page