Digital Multiplexers:
A multiplexer is a logic device that switches one of many input lines to a single common output line.

Multiplexing is a general name for transmitting one or more analog or digital signals over a common transmission line at different times or speeds, and the device we use to do this is called a multiplexer.
The data input that will flow to the output depends on the select line value.
Only one input at a time can pass to the output.
if select is 00: A will pass
if select is 01: B will pass
if select is 10: C will pass
if select is 11: D will pass

Multiplexer Application
There are many applications for MUX and in digital design signal routing MUX is a crutial component