Here are the definitions for these terms, summarized from Robert Harley's book "The Complete Guide to High-End Audio":

1. Resistance and impedance are terms that are sometimes used interchangably to describe the opposition to current flow in an electrical circuit. They are not quite the same, however, since impedance differs from resistance in that impedance implies that the load is not a simple resistance, but a combination of resistance, inductive reactance, and capacitive reactance (more on these terms in a moment). Impedance is the opposition to flow in an AC current as specified in ohms, and represented by the symbol "Z". Impedance to an AC current is analogous to resistance, which occurs in a DC current. In other words, if the current is AC, the opposition to current flow is impedance; if the current is DC, then the opposition to current flow is resistance. Hence, because loudspeakers (as one example) are driven by AC signals, they have impedance, not resistance. Impedance is an important factor for speaker cables, as low impedance is desirable. Speaker cables with high impedance alter the frequency response of the audio signal, usually causing the frequency response to fall at the low and high ends of the audible spectrum.

2. Capacitance (or capacitive reactance) is an important factor for interconnects, particularly when long runs are used. In simple terms, capacitance involves the storage of electrical energy (by the dielectric/insulation), which may be released slighly out-of-synch with the actual signal, thereby "smearing" the integrity of the signal. Capacitance is also used as a term to describe the amount of energy stored in power supply capacitors (usually expressed in fractions of farads, such as picofarads or microfarads), although the amount of energy stored and released by the power supply caps may also be measured in joules. Capacitance is an important factor with interconnects, where low capacitance is desirable so the energy stored and released by the IC is minimal. It's also relevant because capacitive reactance increases as the frequency decreases, thereby acting to reduce low frequency signal transmission.

3. Inductance (more correctly, reactive inductance) is the term to describe an electronic component that increases its opposition to current flow as the frequency increases (e.g., many loudspeaker crossovers use a large inductor on the woofer to filter out high frequencies).

To summarize, the ideal interconnect would have low impedance (which is usually inverse to capacitance, so low impedance IC's will have higher capacitance). Conversely, the ideal speaker cable will have low capacitance (and, inversely, higher impedance). The desirable condition for both IC's and speaker cables is low inductance, since you would not want the cable to change the frequency response as the frequency itself increases.

At the risk of belaboring these points, it's useful to know that speaker crossovers are comprised of both capacitors (which become more reactive at low frequencies, and therefore are used to contour bass response) and inductors (which become more reactive at high frequencies, and are therefore used to contour the high frequencies). These properties of capacitors and inductors can hence be exploited to perform specialized functions in audio circuits, such as the crossover function just described.

With any luck, Sean will see this thread and respond with a better explanation than the one I've posted.

1. Resistance and impedance are terms that are sometimes used interchangably to describe the opposition to current flow in an electrical circuit. They are not quite the same, however, since impedance differs from resistance in that impedance implies that the load is not a simple resistance, but a combination of resistance, inductive reactance, and capacitive reactance (more on these terms in a moment). Impedance is the opposition to flow in an AC current as specified in ohms, and represented by the symbol "Z". Impedance to an AC current is analogous to resistance, which occurs in a DC current. In other words, if the current is AC, the opposition to current flow is impedance; if the current is DC, then the opposition to current flow is resistance. Hence, because loudspeakers (as one example) are driven by AC signals, they have impedance, not resistance. Impedance is an important factor for speaker cables, as low impedance is desirable. Speaker cables with high impedance alter the frequency response of the audio signal, usually causing the frequency response to fall at the low and high ends of the audible spectrum.

2. Capacitance (or capacitive reactance) is an important factor for interconnects, particularly when long runs are used. In simple terms, capacitance involves the storage of electrical energy (by the dielectric/insulation), which may be released slighly out-of-synch with the actual signal, thereby "smearing" the integrity of the signal. Capacitance is also used as a term to describe the amount of energy stored in power supply capacitors (usually expressed in fractions of farads, such as picofarads or microfarads), although the amount of energy stored and released by the power supply caps may also be measured in joules. Capacitance is an important factor with interconnects, where low capacitance is desirable so the energy stored and released by the IC is minimal. It's also relevant because capacitive reactance increases as the frequency decreases, thereby acting to reduce low frequency signal transmission.

3. Inductance (more correctly, reactive inductance) is the term to describe an electronic component that increases its opposition to current flow as the frequency increases (e.g., many loudspeaker crossovers use a large inductor on the woofer to filter out high frequencies).

To summarize, the ideal interconnect would have low impedance (which is usually inverse to capacitance, so low impedance IC's will have higher capacitance). Conversely, the ideal speaker cable will have low capacitance (and, inversely, higher impedance). The desirable condition for both IC's and speaker cables is low inductance, since you would not want the cable to change the frequency response as the frequency itself increases.

At the risk of belaboring these points, it's useful to know that speaker crossovers are comprised of both capacitors (which become more reactive at low frequencies, and therefore are used to contour bass response) and inductors (which become more reactive at high frequencies, and are therefore used to contour the high frequencies). These properties of capacitors and inductors can hence be exploited to perform specialized functions in audio circuits, such as the crossover function just described.

With any luck, Sean will see this thread and respond with a better explanation than the one I've posted.