Random forests is an ensemble algorithm. Ensemble algorithms use several algorithms together to improve predictions. Scikit-learn has several ensemble algorithms, most of which use trees to predict. Let's start by expanding on decision tree regression with several decision trees working together in a random forest.
A random forest is a mixture of several decision trees, where each tree provides a single vote toward the final prediction. The final random forest calculates a final output by averaging the results of all the trees it is composed of.
