Formal: The formal type of machine learning is a computer program that learns from experience in respect to some task and increases performance based on that experience
Informal: The informal involves giving computers the ability to learn without explicitly programming the capability
Unsupervised learning is the reverse of supervised learning where the correct answers are unknown. For example:
Clustering Algorithm: Used to find patterns in datasets and then group that data into different coherent clusters
Market Segmentation: Targeting customers based on regions, likes, dislikes, when the consumer makes purchases, etc. This is considered targeted marketing.