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It is difficult to be specific without some context, but every wire, device or component has capacitance and inductance. So, if you choose a resistor, you don't get a perfect resistor, you get one with a bit of capacitance and inductance. That capacitance/inductance is 'parasitic'.
Noise cancellation, or active noise control,
involves recording the single cycle of
a sound wave and transposing a wave with
the same amplitude but opposite polarity,
the anti-phase. The two waves will have the
same frequency but opposite phases. As the
waves interfere with one another they create
a new wave and cancel out, much like
a standing wave. Noise cancellation allows
for any sound with a continuous wave, like
that of a fan, to be blocked selectively by
programming the recording device to the
specific frequency of disturbance.
Noise cancellation, or active noise control,
involves recording the single cycle of
a sound wave and transposing a wave with
the same amplitude but opposite polarity,
the anti-phase. The two waves will have the
same frequency but opposite phases. As the
waves interfere with one another they create
a new wave and cancel out, much like
a standing wave. Noise cancellation allows
for any sound with a continuous wave, like
that of a fan, to be blocked selectively by
programming the recording device to the
specific frequency of disturbance.
A parasitic is an undesired effect due to the physical nature of a device. As keith mentioned, all real devices have parasitic effects inherent to them. A resistor may be perfect and operate up to infinite frequencies in circuit analysis or simulation, but when you have a real chip resistor, it will have additional effects due to it's physical geometry.
For example, a SMT chip resistor will have parasitic capacitance in parallel, and some series inductance. The metal leads of the package are the key contributors. The metal leads being close together develops some capacitance, and the length of metal to carry current from the metal trace on the PCB up to the thin-film resistive material inside the chip generates some inductance. Below is a resistor model showing the key contributors. **broken link removed**
Additionally, you can have shunt capacitance to ground on each lead, since the leads are in parallel with the groundplane, so you have (small) parallel plate capacitors.
This happens with all devices, and must be taken into account when designing at high frequencies and over wide bandwidths.
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