What is the difference between supervised learning and unsupervised learning?

Supervised learning is when the data you feed your algorithm with is "tagged" or "labelled", to help your logic make decisions.

Example: Bayes spam filtering, where you have to flag an item as spam to refine the results.

Unsupervised learning are types of algorithms that try to find correlations without any external inputs other than the raw data.

Example: data mining clustering algorithms.