Machine Learning refers to the general field of study that deals with automated statistical learning and pattern detection by non-biological systems. It is a sub-domain of General Artificial Intelligence that specifically deals with data analysis, modeling and prediction through the knowledge extracted from the previous (training) samples.
Most common algorithms
When considering the most used algorithms in Machine Learning, it's possible to create a simple taxonomy based on their most prominent characteristics.
The most widely distinction is usually made between the generative (k-NN, k-means clustering, …) vs discriminative (SVM, LDA, …) ones – while the first is able to spontaneously (in a unsupervised way) generate different categories based purely on the data structure, the second kind is only able of distinguishing previously learned classes.
These same algorithms can be static (such as Neural Networks), disregarding the temporal\sequential characteristics of the data, or dynamic (Hidden Markov Chains, for instance), able to account for those temporal dynamics.
The third and last big difference refers to its sensitivity to the variance within the data, that is, the algorithm’s ability to model the training data very closely or more losely (which can actually by a problem commonly referred to as overfitting).
The use of Machine Learning has been widespread since it’s formal definition in the 50’s. The ability to explore the data structure and make predictions based on previous behavior has been extensively used in areas such as market analysis, natural language processing or even brain-computer interfaces. Amazon’s titles suggestion, for instance, is an example of a deep and recursive system for modeling previous buys and generating possible hypothesis from that data.