The median divides ordered data into two equal halves. Q1 (first quartile) separates the lowest 25%, Q3 (third quartile) separates the highest 25%. Interquartile Range (IQR) = Q3 - Q1 measures spread of the middle 50% and is resistant to outliers. For grouped data, the same interpolation formula applies with N/4 and 3N/4 replacing N/2. Semi-interquartile range = IQR/2. While JEE rarely tests quartiles directly, understanding them helps with data interpretation MCQs. The median is especially useful for skewed distributions where the mean is pulled toward outliers.