An "artificial" harmonic is distinguished from a "true" harmonic only in the method by which it is performed. Typically artificial harmonics are played on an electric guitar because they are typically high order harmonics which would be nearly inaudible without the huge amounts of gain a typical guitar amp can deliver, though they may be performed on any stringed instrument that you can manage to play with a plectrum.
To play an artificial harmonic, hold your guitar pick between your thumb and index finger as you normally would, except allow only a tiny amount of the pick to protrude past the flesh on the side of your thumb. When you strike a string, immediately after, nearly simultaneously, you want the edge of your thumb to strike the string as well. The idea is, you want your thumb to very briefly mute the string as you play it right at a node so that the string is stopped from vibrating except at harmonics which naturally have a node where your thumb has hit it. (It sounds more difficult than it actually is, it's really quite easy once you get the knack.) So, the location on the string where you pluck it is important. There are typically some nice ones to be found by plucking near the neck pickup. To find them, you can rapidly pluck the string in the manner described above while moving your plucking hand slowly from the bridge towards the neck. As you pass over various nodes, you will hear different harmonics.
In contrast, "true" harmonics, or just "harmonics" are performed by damping the (usually unfretted) string at node points with the fretting hand. Artificial harmonics are easier to play when the strings are fretted, since the fretting hand is not involved in the production of the harmonic.