The tracking pixel allows to track how many times a webpage have been viewed (visits) or how many time an email was opened (opens).
Tracking pixel is a little piece of code containing an
image (1 pixel * 1pixel dimension) that should be inserted in the pages
of your website or in the email you send.
Tracking pixels could be used also track conversion. You will able to
know which user, from which page of you site, or from which email or
blog lead to a conversion, also if he just visited the page and did not
clicked on your tracking link.