Question: Ive seen television programmes and videos of buddhist shaolin monks who perfom incredible techniques such as breaking iron bars with their heads, impaling themselves with spears, throwing needles through glasses windows etc.

It was said that these monks create, harness and use Qi Energy which makes it possible for them to perform these techniques. I have two questions:

What is this Qi Energy?

Is it a strong and profound level of concentration like the Jhanas in Theravada Buddhism?

Thank you for your time.

Answer: 
When Dave's answer says "It's a metaphor", then I guess he mean something like this.

When you're a beginner, learning, a teacher might try to teach you to change your posture slightly, to stand straighter, to better balance your head on your spine, and your spine on your hips, and so on.

When they do that they might say to you something like, "Imagine that your head and body are hanging suspended by a rope" (or imagine that energy is projecting from the top of your head to the sky).

When you hear that and try to make sense of it and comply, then you might stand straighter like they wanted you to. In future when they want to remind you it might become a verbal short-hand command – "Remember: a thread, above your head".

Now in one sense there is no physically observable thread: it's not a real thread, the thread is a "metaphor", or an analogy that intended to help you to comply. On the other hand it may actually have an effect: in that it helps you to stand straighter... :-)
Qi is a metaphor

Qi is cultish social pressure

Qi is a hand-waving pre-scientific explanation for basic bodily functions

Qi is the object of irrational fixation for people who cling to magical thinking

Qi is cover for ludicrous lies about "miracles" like teleportation and flying whose most impressive feature is deft avoidance of proof

Qi is, sometimes, a vague description of that amalgam of trained athleticism, learned technique, and plain concentration that allows one to accomplish feats of strength