Definition of "Pest" :
noun: any unwanted and destructive insect or other animal that attacks food or crops or livestock etc.
"He sprayed the garden to get rid of pests."
noun: a persistently annoying person
noun: any epidemic disease with a high death rate
noun: a serious (sometimes fatal) infection of rodents caused by Yersinia pestis and accidentally transmitted to humans by the bite of a flea that has bitten an infected animal