A portlet is a small chunk of secondary content that is often assisting or functional, like a navigation or information on related items. Most of the time they grace one of the two colums that are available on most sites. This does seem to indicate that portlets are a subtype of pagelets but for various usage reasons its generally beneficial to regard them as separate and simply include portlets using a pagelet.
Disclaimer: This section is for information purposes only posted by the public. If you feel the information is incorrect, please send us an email to webmaster at computeruser dot com.