Looking at the online and other popular dictionaries such as Merriam Webster and Oxford Advance Learners’ Dictionary etc., only simple explanations are found such as “Public speaking is the art or practice of making speeches to large audiences”.
The definition given on Wikipedia keeps changing as more and more people refine it. Hopefully there will come a day when no one wants to change it any more. But, if leave the limiting definitions aside, then the vastness of its general meaning will emerge.
In fact every time you open your mouth to say something to three or more people, it is public speaking. Settings can range from talking to informal gatherings of couple of neighbors on important issue of the day to formal settings where people are gathered to hear your announced speech.
In fact, gossiping in which many people talk to achieve a common objective (most of the time character assassination of someone known to all participants) is the most effective form of interactive public speaking.
Appearing for an interview apposite a panel of experts, participating in group discussions and collecting your staff for a motivation dose are all public speaking.
Overcome fear of public speaking, if any, and make an impact on every opportunity to speak to public.
So next time you think of "what is public speaking", don't limit your imagination. Consider every opportunity to collectively speak more than two people is public speaking.