What is pitch raising?
If a piano hasn't been tuned for a long time, the pitch may drop below A440. A pitch raise corrects this before standard tuning can hold.
If your piano has not been tuned for a long time, the pitch may have dropped below the standard Concert Pitch (A440). In this case, it will need additional tuning — called a pitch raise — before it can be tuned and remain stable.
Depending on the condition and service history of the piano, more than one pitch raise may be required before the piano can hold its tune. Some very old pianos are no longer capable of supporting the string tension required to maintain A440 concert pitch.
If you suspect your piano needs a pitch raise, consult a qualified piano technician for assessment.