what does it mean selec="cos2 9" in plot()

#1
Hello;
l want to know the function and the meaning of the argument select="cos2 9"
what does it mean cos2 ?

here is my function plot


res<- PCA(d,quali.sup<- c(1,10)) and d is mydata

plot(res,cex=0.9,shadow=F,habillage=10,invisible=c("ind.sup","quali"),select="cos2 9",unselect=1)

Thank you for your consideration
 
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