What is a hobby? Wikipedia definition: Hobbies are practiced for interest and enjoyment, rather than financial reward. Engaging in a hobby can lead to acquiring substantial skill, knowledge and experience. However, personal fulfillment is the aim.
Examples from Wikipedia or at least some of the most common are collecting stamps, baseball cards, magazines, stamps.

Many hobbies involve performing by the hobbyist, such as singing, acting, juggling, magic, dancing and other performing arts. And then there are the creative arts:woodworking, building a computer from scratch, moviemaking, jewelry making, playing a musical instrument, software projects, artistic projects (such as drawing, painting, etc.), creating models out of card or paper called papercraft up to higher end projects like building or restoring a car, or Photography.

While these may just be for the enjoyment of the hobbyist, they sometimes have potential to be a small business.

Outdoor pursuits can be loosely considered to be the group of sports and activities which are dependent on the great outdoors, incorporating such things as hill walking, hiking, backpacking, canoeing, kayaking, climbing, caving, and arguably broader groups such as watersports and snowsport... of course some may argue that a sport is a sport and not a hobby. But this could easily be turned around if you re-read the definition again.

So you decide to get into photography... because years ago you were heavy into photography to the point of having your own darkroom to develop your own pictures. But life got in the way of your hobby and you got caught up in your work. Now several years later you borrowed a Nikon DSLR and fell in love again... how could so much time have passed by....then you are introduced to the new digital darkrooms such as photoshop and lightroom...all the barriers from the past are lifted in an instant....not enough film, printing costs, lighting, equipment.....having to wait for the film to be developed before you know if that effect worked.... to be continued....