Gradient Descent (video from StatQuest) is the workhorse behind most of Machine Learning. When you fit a machine learning method to a training dataset, you're probably using Gradient Descent. It can optimize parameters in a wide variety of settings.

Gradient Decent starts with a guess for the value and then goes into a loop that improves the guess one small step at a time. Although Gradient Decent takes longer than an analytical solution, it is very often used in ML because it can give solutions to situations where there are no analytical solutions, including Deep Neural Networks.
