Read through the forum threads and you are sure to reach an impossible consensus of contradictions. I could tell you what it is, but then someone else may tell you something else. Practice it to find out what it is, thats the best way. Best, Syd
Although there are widely varied and conflicting opinions, most people agree the internal arts focus on combining health aspects with martial art practice, and in exploring ways to put more power/control into your movements (e.g. breathing methods, breaking movements down to their elements, refining body mechanics, concentration exercises, etc). Probably a little more vague than you were hoping but any more detailed and I would start stepping on toes.
i think the internal martial arts can be defined as using energy(jing) as a means of fighting instead of muscle power. not exactly a detailed answer sorry you'd best be off reading some writing on the subject.
Or defined as using 'core' power (and power generated from the ground/legs/waist) as the main power/energy source, usually with a lot of control/follow-through throughout the movements.
being aware of body mechanics to derive a little power from several sources adding up to a big deal rather than relying on one big muscle
It's spreading the force around. If I was mechanically minded I'd relate it to pulley and gear systems - each gear/joint/muscle has to do less work to achieve a huge effect if the whole thing is coordinated.
Internal Arts is..... .....when you do not rely on muscular, age, size , oain tolerance superiority but on natural body mechanics and Chi to fight. Nice analogy: An External Martial Artist who finds himself on a raft drifting in a lake , will try to swim ashore. An Internal Martial Artist will stay on the raft and work out the natural water currents and wind directions and using minimum force "sail" his way ashore.