I prefer to use the phrase ‘giving a talk’ because ‘Public Speaking’ sounds much too grand for what I do, even though it is, in reality, just as accurate. Even if you speak to three people, they count as ‘the public.’ However, when a complete novice is presented with the unaccustomed task, ‘giving a talk’ sounds less frightening.
It is the same when speaking about any subject to an audience that has not encountered it before. Unless you are imparting detailed knowledge at a college lecture or training session, use simple explanations and everyday language where possible. At a talk given by a local amateur astronomer, we had the concept of a Light-year explained in terms of scaled down distances on the earth. Distances we can understand could give us some idea of the enormous scale involved in the universe.
Do not treat your audiences like children (unless they are, but even they should not be treated like idiots) but understand that they are not familiar with jargon, concepts, abbreviations etc. It is infuriating when a speaker talks in jargon and abbreviations that sound like a foreign language, which they are! Always explain any specific language that you might need to use. Make sure your audience knows what you mean.