The term 'audience' is probably one of the most often used terms in media. We don't tend to analyse an audience apart from at a distance, we make generalisations about it and we never seem to think of ourselves as a part of one.
When we actually start analysing the idea of 'it', we see that is in fact not an 'it' but, depending on where we are standing and why we look it is a collection of different things. Media texts are constructed with an audience in mind- they are made specifically for us (the audience). In certain cases they try to construct the audience, particularly in the case of propaganda.
My own opinion is that an audience is a group of people, or an individual, that consume a media text and interpret it in their own way depending on many different factors (e.g. Age, Gender).