Linear Regression
Linear Regression is one of the most fundamental Regression techniques used in Machine Learning.
A "training set" of data is used to create the model. The model created is a straight line (hence linear) that has the lowest possible error with the training set. The model can then be used to predict new, unseen data.
It is used as a basis for more complicated techniques such as Lasso and Ridge regression.
Here is an example of how to do Linear Regression by hand:
Linear Regression Example