Lifestyle photography is described as "... a kind of photography which mainly aims to capture portrait/people in situations, real-life events or milestones in an artistic manner and the art of the everyday."
It is a genre of photography that has really sprung up the last several years or so. It's been around for much much longer, but when I look back at old works from photographers it wasn't something that one was hired to do regularly, but armature and professional alike had albums filled with special moments from their own lives. Celebrities and presidents would call someone in to have photos to release to the public, but in general the average Joe did not hire a professional to come follow them for a few hours in their day.
I am not a professional lifestyle photographer. In fact, I rarely do it. However, when I do take those candid just for fun moments in my life I become a lifestyle photographer. Just for a few moments. This is because what I do fits the definition of lifestyle photographer because as a photographer I am an artist. So I "aim to capture people or milestones in an artistic manner." with the little bit of knowledge of photography I have. You know what though? With the invention of cell phone cameras and even better point and shoots we can all capture those special random moments.
"The best camera is the one you have with you." I don't know who said it first, but it's true. Your shots don't have to be perfect, or professional, sometimes they don't even have to be in focus. As long as it evoke an emotion or memory.