A tag is a (relevant) keyword or term associated with or assigned to a piece of information (e.g. a picture, article, or video clip), thus describing the item and enabling keyword-based classification of information for the purpose of retrieval.Wikipedia
Tagging has been introduced to this site to allow resource owners and other site users to describe resources using keywords and phrases. Over time, and as the extent of the tagging increases, this will assist other users who are searching for relevant projects and other content.
Tags can be in any language, and can consist of single or multiple words (up to a maximum of 64 characters). Where tags have been applied to a project, those tags will be displayed on the main project page and in searches for projects. The number of times a particular tag has been applied to a project will be indicated by the text size of the displayed tag.