If you are the fourth tallest person in a group of 20, then 80% of people are shorter than you. That means you are at the 80th percentile. If your height is 1.85m then "1.85m" is the 80th percentile height in that group.
Each dataset has three quartiles, which are the percentiles that divide the dataset into fourparts:
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.
A total of 10,000 people visited the shopping mall over 12 hours. The 30th percentile occurs after about 6.5 hours. The visits at 11 hours were about 9,500, which is the 95th percentile.