An integrated circuit is a semiconductor wafer containing thousands or millions of tiny resistors, capacitors, and transistors. ICs can function as amplifiers, oscillators, timers, counters, memory, or processors. ICs are categorized as either linear (analog) or digital. Linear ICs have continuously variable output depending on the input level, while digital ICs operate at only a few defined levels or states. Common digital ICs include logic gates used in computers to process binary data as either low or high states. The document also describes a custom circuit board designed from scratch in Multisim by the author to build electrical circuits.