Heuristics are what are known as cognitive or mental shortcuts that are used to make judgments about a person, object, or situation.  Representativeness heuristics are judgments that are made based on how well a person's characteristics fit with or represent a certain group.  When someone uses a representativeness heuristic, they assume somebody is part of a particular group simply because of their characteristics or behavior.  For example, a blonde, tan, and lean male college student just arrived at New York University.  On the first day of class he wore board shorts and a tank top that said "I love surfing."  The girl sitting next to him assumed he was from California because he had many characteristics of a surfer (i.e., blone hair, tan, lean, wearing board shorts...).

Availability heuristics are mental shortcuts where the individual makes a judgment or assumption based on how easily they can call the information to mind.  The problem or risk with availability heuristics is that they often cause the person to go with that first thought rather than consider alternatives.  For example, let's say that a woman goes to the doctor because she has a bad cough.  Because the doctor had just finished reading an article about a new strain of pneumonia, he immediately wonders if she might have the virus.  Instead of examining the patient and trusting his experience in order to make a diagnosis, he puts her through a series of uncomfortable and time consuming tests only to find out that she had a common cold.

In contrast to heuristics, algorithms consist of a set of procedures or rules that must be followed specifically in order to solve a problem or arrive at a conclusion.