TYPO3 uses pages to organise the structure of a website. This leads to situations where you have a specific page for a feature, e.g. a page “Search” containing the plugin to display search results. Or a page containing the profile of the currently logged in user. Typically links to these pages are scattered all over the website, e.g. within some content elements, inside the page layout like header and within some plugins.
This Blog post explains how to provide the page uid for a specific page, to all three kinds of “content”, where you typically need this information, with three lines of TypoScript.