The 75th percentile refers to the value in a data set that 75% of the values are below. The median splits the data set exactly in half, with half of values falling below and half above. Percentiles split a data set into hundredths, with the 50th percentile being the median. The 75th percentile can be calculated using the formula n = (P/100) * (N+1), where P is the percentile, N is the number of observations, and n is the rank of the percentile.