Question: The RC time constant, also called tau, the time constant (in seconds) of an RC circuit, a irst order RC circuit is composed of one resistor and one capacitor and is the simplest type of RC circuit, and is equal to the product of the circuit resistance (in ohms) and what (in farads)? 

Context paragraphs:
RC time constant: The RC time constant, also called tau, the time constant (in seconds) of an RC circuit, is equal to the product of the circuit resistance (in ohms) and the circuit capacitance (in farads), i.e.

Tau effect: The tau effect is a spatial perceptual illusion that arises when observers judge the distance between consecutive stimuli in a stimulus sequence.  When the distance from one stimulus to the next is constant, and the time elapsed from one stimulus to the next is also constant, subjects tend to judge the distances, correctly, as equal.  However, if the distance from one stimulus to the next is constant, but the time elapsed from one stimulus to the next is not constant, then subjects tend to misperceive the interval that has the shorter temporal interval as also having a shorter spatial interval.  Thus, the tau effect reveals that stimulus timing affects the perception of stimulus spacing.  Time is also a perceived quantity and subject to its own illusions; research indicates that in the tau effect, perceived stimulus spacing follows perceived (phenomenal) time rather than actual (physical) time.

RC circuit: A resistor–capacitor circuit (RC circuit), or RC filter or RC network, is an electric circuit composed of resistors and capacitors driven by a voltage or current source.  A first order RC circuit is composed of one resistor and one capacitor and is the simplest type of RC circuit.  Charge transport behaviour in various complex systems, including battery anodes and fuel cells can be described using models of many-element RC networks.

Pearson–Anson effect: The Pearson–Anson effect, discovered in 1922 by Stephen Oswald Pearson and Horatio Saint George Anson, is the phenomenon of an oscillating electric voltage produced by a neon bulb connected across a capacitor, when a direct current is applied through a resistor.  This circuit, now called the Pearson-Anson oscillator, neon lamp oscillator, or sawtooth oscillator, is one of the simplest types of relaxation oscillator.  It generates a sawtooth output waveform.  It has been used in low frequency applications such as blinking warning lights, stroboscopes, tone generators in electronic organs and other electronic music circuits, and in time bases and deflection circuits of early cathode ray tube oscilloscopes.  Since the development of microelectronics, these simple negative resistance oscillators have been superseded in many applications by more flexible semiconductor relaxation oscillators such as the 555 timer IC.

Ignition coil: An ignition coil (also called a spark coil) is an induction coil in an automobile's ignition system that transforms the battery's low voltage to the thousands of volts needed to create an electric spark in the spark plugs to ignite the fuel.  Some coils have an internal resistor, while others rely on a resistor wire or an external resistor to limit the current flowing into the coil from the car's 12-volt supply.  The wire that goes from the ignition coil to the distributor and the high voltage wires that go from the distributor to each of the spark plugs are called spark plug wires or high tension leads.  Originally, every ignition coil system required mechanical contact breaker points and a capacitor (condenser).  More recent electronic ignition systems use a power transistor to provide pulses to the ignition coil.  A modern passenger automobile may use one ignition coil for each engine cylinder (or pair of cylinders), eliminating fault-prone spark plug cables and a distributor to route the high voltage pulses.

Clamper (electronics): A clamper is an electronic circuit that fixes either the positive or the negative peak excursions of a signal to a defined value by shifting its DC value.  The clamper does not restrict the peak-to-peak excursion of the signal, it moves the whole signal up or down so as to place the peaks at the reference level.  A diode clamp (a simple, common type) consists of a diode, which conducts electric current in only one direction and prevents the signal exceeding the reference value; and a capacitor which provides a DC offset from the stored charge.  The capacitor forms a time constant with the resistor load which determines the range of frequencies over which the clamper will be effective.

Pierce oscillator: The Pierce oscillator is a type of electronic oscillator particularly well-suited for use in piezoelectric crystal oscillator circuits.  Named for its inventor, George W. Pierce (1872-1956), the Pierce oscillator is a derivative of the Colpitts oscillator.  Virtually all digital IC clock oscillators are of Pierce type, as the circuit can be implemented using a minimum of components: a single digital inverter, one resistor, two capacitors, and the quartz crystal, which acts as a highly selective filter element.  The low manufacturing cost of this circuit, and the outstanding frequency stability of the quartz crystal, give it an advantage over other designs in many consumer electronics applications.

RL circuit: A resistor–inductor circuit (RL circuit), or RL filter or RL network, is an electric circuit composed of resistors and inductors driven by a voltage or current source.  A first-order RL circuit is composed of one resistor and one inductor and is the simplest type of RL circuit.

Open-circuit time constant method: The open-circuit time constant method is an approximate analysis technique used in electronic circuit design to determine the corner frequency of complex circuits.  It also is known as the zero-value time constant technique.  The method provides a quick evaluation, and identifies the largest contributions to time constants as a guide to the circuit improvements.

Relaxation oscillator: In electronics a relaxation oscillator is a nonlinear electronic oscillator circuit that produces a nonsinusoidal repetitive output signal, such as a triangle wave or square wave.  The circuit consists of a feedback loop containing a switching device such as a transistor, comparator, relay, op amp, or a negative resistance device like a tunnel diode, that repetitively charges a capacitor or inductor through a resistance until it reaches a threshold level, then discharges it again.  The period of the oscillator depends on the time constant of the capacitor or inductor circuit.  The active device switches abruptly between charging and discharging modes, and thus produces a discontinuously changing repetitive waveform.  This contrasts with the other type of electronic oscillator, the harmonic or linear oscillator, which uses an amplifier with feedback to excite resonant oscillations in a resonator, producing a sine wave.  Relaxation oscillators are used to produce low frequency signals for applications such as blinking lights and electronic beepers and in voltage controlled oscillators (VCOs), inverters and switching power supplies, dual-slope analog to digital converters, and function generators.

Supporting paragraphs: RC time constant RC circuit
Answer: circuit capacitance