This presentation introduces 7-segment decoders. It defines a decoder as a logic circuit that activates one output corresponding to a binary input number. A 7-segment decoder is used to display decimal numerals on a 7-segment display, with each segment and dot controlled by a common electrode. The presentation explains the working principle of a 7-segment decoder and includes a logic diagram, truth table, and applications such as in digital clocks and calculators. Limitations are that it can only display 0-9 and a few letters, and uses many logic gates.