During interpersonal communications, two or more people carry on a private conversation. This is the sort of talk you might have at home with your spouse or your children. It could also happen between two close friends in a private setting.
Person to person communication is similar to interpersonal in that it is usually a private conversation. However, person to person communication, as the name implies, takes place between no more than two individuals, either in person or over the phone. In this type of speech communication, both individuals usually contribute to the conversation, rather than having one dominate.
A group discussion can be considered a specific form of interpersonal communication. Group discussions usually have a goal or some problem the group is trying to address. This sort of speech communication is often used in situations like business meetings, academic presentations and college seminars.
Public communication is a form of speech communication in which an individual or a small group is giving a speech to an audience that is physically present in the room. There are many professions that use this type of communication, such as university instructors, politicians and ministers.
The type of speech known as mass communication is similar to public communication, except that the speaker or speakers are not restricted to only those in the room. Using television, teleconferencing and web broadcasts, a speaker using mass communication can in theory reach a sizable portion of the world's population.