Fajing is probably the most incorrectly defined concept in Taiji practice.
Most people can NOT experience Fajing unless you train with a true master that understand this concept.
Some masters incorrectly define it as an effect after an attack. This is so incorrectly wrong that confuse some students to the wrong path of understanding Fajing.
Fajing is the ABILITY of the body to create powerful projective forces from any parts of the body. Fajing requires the body to be trained properly to be totally relax and conditioned correctly.
Higher level fajing teaches you to narrow an attack to the size of a small area in the body. GM Yang Jwing Ming taught us this concept of precision fajing through candle punching.