CD4051 is an 8 channel analog multiplexer & demultiplexer, controlled by digital signal. So, they are commonly referred as Digitally-controlled Analog Switches.
It has low ON impedance and very low OFF leakage current. It dissipates a very low power over full VDD-VSS & VDD-VEE voltage ranges. eliminatiing channel overlapping and wide ranges of analog signals are its main feature.
It can be used for analog to digital (A / D) as well as digital to analog (D / A) conversions.