Any two points that are not at the same voltage have capacitance between them. So there are many possibilities of parasitic capacitance. The normal idea of parasitic capacitance is capacitance that effects the operation of your circuit in operation. So if you are using a circuit to amplify DC, then a few extra picafarads of capacitance would have no appreciable effect, but if it was a tuned amplifier, it could cause it to oscillate or be tuned at the wrong frequency.
" who is the one that considered first time the concept of parasitic capacitance in the circuits" I do not know, but a fellow called MILLER first noticed an effect, where by capacitance was multiplied by the gain of a circuit, so I guess he had noticed it.
Frank