Stating out..... what is a workout?

What exactly is working out?
I start out this process with curiosity, and right now i'm wanting to know more about workouts in general, and also what ways people these days exercise and incorporate those workouts into their daily routines. I have several questions all in regards to workouts, but for now we'll just try to determine what exactly fitness professionals consider a workout. Fitness in general seems to be common place these days, and i find that to be interesting. Let's explore! I start this project with a search on the auraria campus library searching for "fitness." My first article is the following:
Fitness Culture: Gyms and the Commercialisation of Discipline and Fun. Roberta Sassatelli. Palgrave Macmillan, 2010. Palgrave Connect. Palgrave Macmillan. 11 Mar 2012.

 This book begins to answer my first question. The author looks at fitness not from a physical perspective, but from a mental perspective. She discusses fitness from a sociological perspective and ways in which a person "needs" to feel fit, and looks at personal experiences at the gym to help describe those personal "needs." The author looks at how fitness culture is much more broad than just the gym. This is a good place to start! maybe my qwest for workout knowledge first must start out with fitness culture?

Before i answer that question, i feel it's important to define fitness and physical activity. One article defines physical activity as "movement via skeletal muscles, that results in energy expendiatures, planned, physical, and repetitive bodily movement."
 Caspersen, C., K. Powell, and G. Christenson. "Physical activity, exercise, and physical fitness: definitions and distinctions for health-related research." . N.p., 1995. Web. 11 Mar 2012.