An encoder is a multiplexer without its single output line. It is a combinational logic function that has 2n (or fewer) input lines and n output lines, which correspond to n selection lines in a multiplexer.
The n output lines generate the binary code for the possible 2n input lines. Let us take the case of an octal-to-binary encoder. Such an encoder would have eight input lines, each representing an octal digit, and three output lines representing the three-bit binary equivalent.
