Input changes a pin's data direction to input.
In assembly language, converting a pin to input requires writing a 1 to the corresponding bit of the port's TRIS register. The second definition applies to instructions like Pwm that perform their output function, then disconnect to avoid interfering with the operation of other circuitry. In the case of Pwm, disconnecting the output dri ver allows a capacitor to retain the voltage level set by the burst of pulse-width modulation. They recommend periodically rewriting the TRIS registers, just in case.