Plain English Meaning
Flying an instrument approach for training rather than because the weather requires it. The pilot rehearses the approach to stay sharp, with another pilot watching for traffic or with help from air traffic control.
Full Definition
Instrument approach procedures flown for training or proficiency rather than to land from actual instrument conditions. Practice approaches may be conducted in visual conditions with a safety pilot or under instrument flight rules with air traffic control, and they are used to build and maintain the skills required to fly an approach to landing minimums.