1 To mark in some distinctive fashion any node in a data structure that has been traversed. Using this technique precautions can be taken against revisiting nodes, e.g. in a circular list.
2Short for tag field. A field that is used to discriminate between variants of the same type.
3 A set of characters used to delineate certain types of text in a markup language. For example, in HTML bold text would normally be indicated by using the tags <b> and </b>, as in “this word is <b>bold</b>.”