In formal language theory, the terminal yield (or fringe) of a tree is the sequence of leaves encountered in an ordered walk of the tree.

Parse trees and/or derivation trees are encountered in the study of phrase structure grammar

Phrase structure grammar

The term phrase structure grammar was originally introduced by Noam Chomsky as the term for grammars as defined by phrase structure rules, i.e. rewrite rules of the type studied previously by Emil Post and Axel Thue...

s such as context-free grammar

Context-free grammar

In formal language theory, a context-free grammar is a formal grammar in which every production rule is of the formwhere V is a single nonterminal symbol, and w is a string of terminals and/or nonterminals ....

s or linear grammar

Linear grammar

In computer science, a grammar is linear if it is context-free and all of its productions' right hand sides have at most one nonterminal.A linear language is a language generated by some linear grammar.-Example:...

s. The leaves of a derivation tree for a formal grammar G are the terminal symbols of that grammar, and the internal nodes the non-terminal or variable symbols. One can read off the corresponding terminal string by performing an ordered tree traversal

Tree traversal

In computer science, tree-traversal refers to the process of visiting each node in a tree data structure, exactly once, in a systematic way. Such traversals are classified by the order in which the nodes are visited...

and recording the terminal symbols in the order they are encountered. The resulting sequence of terminals is a string of the language L(G) generated by the grammar G.