This circuit represents a 4-bit bus that is enabled using 4 CMOS tri-state buffers. The bits along the top are the enable bits for each of the four bit bus lines along the left.
When each enable bit is set to 1, the bus lines along the left are permitted to flow freely from the connection points where the oscilloscope lines are located. When the enable bits are set to 0, that bus line is disabled and its state is called hi-Z for high impedance because it is essentially an open circuit at that point.
