The definition above is very broad. It is based on ideas by Georg Jellinek (1851-1911). Other people had other ideas:
ð ə WORD_BOUNDARY d ɛ f ɪ n ɪ ʃ ə n WORD_BOUNDARY ə b ʌ v WORD_BOUNDARY ɪ z WORD_BOUNDARY v ɛ ɹ i WORD_BOUNDARY b ɹ ɔ d WORD_BOUNDARY ɪ t WORD_BOUNDARY ɪ z WORD_BOUNDARY b eɪ s t WORD_BOUNDARY ɔ n WORD_BOUNDARY aɪ d iə z WORD_BOUNDARY b aɪ WORD_BOUNDARY d̠ʒ ɔ ɹ ɡ WORD_BOUNDARY d̠ʒ ɛ l aɪ n ə k WORD_BOUNDARY w ʌ n WORD_BOUNDARY θ aʊ z ə n d WORD_BOUNDARY eɪ t h ʌ n d ɹ ɪ d WORD_BOUNDARY f ɪ f t i WORD_BOUNDARY w ʌ n WORD_BOUNDARY d æ ʃ WORD_BOUNDARY n aɪ n t iː n h ʌ n d ɹ ɪ d WORD_BOUNDARY ɪ l ɛ v ə n WORD_BOUNDARY ʌ ð ə ɹ WORD_BOUNDARY p iː p ə l WORD_BOUNDARY h æ d WORD_BOUNDARY ʌ ð ə ɹ ɹ WORD_BOUNDARY aɪ d iə z WORD_BOUNDARY