The 555 timer IC gets its name from the three 5 kilo-ohm resistors in its internal circuit. It consists of two comparators, two transistors, a flip-flop, and an output stage. The comparators reference voltages of 1/3Vcc and 2/3Vcc are produced by a voltage divider of three equal 5k resistors connected in series. The 555 timer can operate in three modes - astable, monostable, and bistable - and is used for applications like precision timing, pulse generation, time delay generation, and sequential timing.