This document provides an overview of least squares approximation, a linear algebra technique for fitting a linear or polynomial model to data. It explains that least squares approximation finds the "best fit" line or curve to describe the relationship between variables by minimizing the error between predicted and actual values. The document also discusses how the least squares method works by estimating coefficients to create a linear or polynomial expression that best describes the data using techniques like minimizing the error vector and using the inverse and transpose of matrices. Real-world applications to fields like econometrics are also briefly mentioned.