Precision Rectifier
The precision rectifier or also called super diode.
When the VIN<0, there is a negative voltage on the diode, so it works like an open circuit, no current flows through the load, and the output voltage is zero.
When VIN>0, it is amplified by the operational amplifier, which switches the diode on. Current flows through the load and, because of the feedback, the output voltage is equal to the input voltage.
\[VOUT = max(VIN,0)\]