Portlets在Web门户上管理和显示的可插拔的用户界面组件。Portlet产生可以聚合到门户页面中的标记语言代码的片段，如HTML，XML等。通常，根据桌面隐喻，一个门户页面显示为一组互相不重叠的portlet窗口，其中每一个portlet窗口显示一个portlet。因此，可以说一个（或一组）portlet就像一个在门户网站上运行的基于Web的应用进程。 Portlet应用进程的一些例子包括电子邮件，天气预报，论坛和新闻等。

Portlet标准的目的是使开发人员开发出的portlet可以插入到任何支持该标准的门户网站。

Portlets are pluggable user interface software components that are managed and displayed in a web- or enterprise- portal.

Portlets produce fragments of markup (HTML, XHTML, WML) code that are aggregated into a portal. Typically, following the desktop metaphor, a portal page is displayed as a collection of non-overlapping portlet windows, where each portlet window displays a portlet. Hence a portlet (or collection of portlets) resembles a web-based application that is hosted in a portal.