Riyaa' is when one intends to gain the people's pleasure when drawing close to Allah Tala. It is action of the heart and not the action of the tongue. Riyaa is the pure intention and not the the aim, since the aim in this case is the pleasure of the people however the intention maybe to please Allah tala. For example: One can draw closer to Allah Tala in worships ('Ibadaat) or many other things. So the one who prolongs his prostration so that people can see him is showing off. The one who writes an article so that people say he is a scholar is showing off. The one who gives a lecture to impress the poeple is showing off. The one who gives a khutbah so people say he is a good khateeb is showing off. The one who wears rags so people say he is simple is showing off. The one who grows a beard and wears jalbiyya so people say he is following sunah is showing off. The one who eats baked beans so people say he is ascetic is showing off. The one who walks with head down so people think he is pious is showing off. The one who carries a small copy of the Quran and reads it in public to show people is showing off