A syntactic category is a set of words and/or phrases in a language which share a significant number of common characteristics. The classification is based on similar structure and sameness of distribution (the structural relationships between these elements and other items in a larger grammatical structure), and not on meaning. In generative grammar, a syntactic category is symbolized by a node label in a constituent structure tree.
Bickford, J. Albert, and John Daly. 1996.A course in basic grammatical analysis. 3rd preliminary edition. Dallas, TX: Summer Institute of Linguistics.