Terminology
A syntactic tree represents the syntactic relations within a sentence hierarchically by means of
terminal (lexical) nodes/constituents, which cannot be expanded, and
non-terminal nodes/constituents, which allow further expansion. By convention, constituents can be defined as:
mother,
sister or
daughter
nodes/constituents. Depending on their degree of obligatoriness, they are subdivided into
complements (obligatory constituents) and
adjuncts (optional constituents).