Meaning : (figurative) people whose criticisms are regarded as irrelevant or insignificant (resembling uneducated people who throw peanuts on the stage to express displeasure with a performance).
Example :
He ignored complaints from the peanut gallery.
Meaning : Rearmost or uppermost area in the balcony containing the least expensive seats.
Synonyms : family circle, second balcony, upper balcony