Each dataset has three quartiles, which are the percentiles that divide the dataset into four parts:
First Quartile is the sample 25th percentile. It divides roughly 25% of the smallest items from the rest of the dataset.
Second Quartile is the sample 50th percentile or the median. Approximately 25% of the items lie between the first and second quartiles and another 25% between the second and third quartiles.
Third Quartile is the sample 75th percentile. It divides roughly 25% of the largest items from the rest of the dataset.