Luzin is a mathematical concept named after the Russian mathematician Nikolai Luzin. It refers to a type of set in the field of real analysis, particularly in the study of measure theory. A Luzin set is a subset of real numbers that can be well-approximated by continuous functions, making it significant in understanding the properties of measurable functions. The concept is often discussed in relation to Lebesgue measure, which is a way of assigning a size or measure to sets of real numbers. Luzin's work contributed to the development of modern analysis and has implications in various areas of mathematics, including topology and functional analysis.