Website tagging is the process of implementing third party tags on a website.
These tags are provided by marketing vendors and partners and are used to display different elements on the page (banners, widgets, social buttons, etc.) and especially to collect data about visitors and context.
Website tagging raises several issues as more and more third party tags are implemented on websites:
coordination with IT teams
delays in marketing operations
page loading time slow-downs
poor visitor experience
conversion attribution and deduplication
potential data leakages
For more details, see third party tag.
To adress these issues, many tag management solutions have emerged and the IAB has released its "Site Tagging Best Practices".