In a chip, resistance (R) is how difficult it is for current to flow. For example, the longer the wire, the higher the resistance. The material also matters: copper wire has more resistance than silver wire. The capacitance (C) is the amount of electrical charge the wire stores.
When a logic gate switches from zero to one, it charges the capacitance in the output wire. R times C (RC) defines how quickly the voltage reaches the required level for the next gate to recognize the pulse.
Narrower interconnecting wires cause resistance to rise; for example, the resistance quadruples when the diameter of a wire is cut in half; however, there is less capacitance. Reducing RC delay is a major design challenge in modern chips. See
chip,
Boolean logic and
chip manufacturing.