* Verb: Describing the action of making a buzzing sound, as in "The bee is buzzing around the flower."
* Adjective: Describing something that is making a buzzing sound or something that is lively and full of activity, as in "The room was filled with buzzing excitement."
* Gerund: A noun formed from a verb, referring to the act of buzzing, as in "The buzzing of the bees was loud."
So, the specific part of speech depends on the context of the sentence!