Quartiles are the values which divide the data set into four equal parts called quarters. Thus there are three quartiles and four quarters.
Similarly the nine values which divide the data set into ten equal parts are called deciles, denoted by D1,D2,...,D9
The 99 values which divide the data into 100 equal parts are called percentiles. They are denoted by P1,P2,P3,......,P99.