Some of my orb pictures
Most orbs are created when light is reflected from dust or dirt or water droplets in the air. You can create orbs by shaking a pillow or cloth in the air and then taking a flash photo with a camera that uses a camera mounted flash. You can also spray water from a spray bottle and achieve the same results.
Many orbs however are not explained so simply and some say they are the energy of spirits or mental energy transmitted by a living being. These orbs are the ones you capture when not using a camera mounted flash, or when using a time exposure. They can also be seen in videos. Orbs with unusual streaks or afterglow are particularly interesting.
All the photos on this page were taken without a flash under more or less ideal conditions. Some are certainly natural phenomenon, particularly the cave photos which may be water droplets even though no flash was used. Others - not so natural. All are interesting though.
In any event - be sure to dismiss all natural causes for an orb before deciding it is unexplainable, and don't dismiss any options for the cause of an orb. Just because one orb is caused by dust doesn't mean all of them are!
Finally, look closely at every orb. You can see many differences in them that can help to classify them. Also, remember that many are out of focus dust particles, and such an image will change its look depending on how out of focus the image is.
There are a lot of good websites on orbs - be sure to look them up. I believe that not all orbs are explainable, but most are. Wikipedia has a good definition of the most common types of orbs the first line reading "Orb artifacts are captured during low-light instances where the camera's flash is used, such as at night or underwater—or where a bright light source is near the camera."
Dust or ghosts? Inspect your orbs and decide for yourself!