A fad or trend is any form of behavior that develops among a large population and is collectively followed enthusiastically for a period of time, generally as a result of the behavior being perceived as popular by one's peers or being deemed "cool" by social or other media. A fad is said to "catch on" when the number of people adopting it begins to increase rapidly. They normally fade quickly once the perception of novelty is gone.

In biochemistry, flavin adenine dinucleotide (FAD) is a redox cofactor, more specifically a prosthetic group, involved in several important reactions in metabolism. FAD can exist in three (or four: flavin-N(5)-oxide) different redox states, which are the quinone, semiquinone, and hydroquinone. FAD is converted between these states by accepting or donating electrons.

Phi Alpha Delta (ΦAΔ or PAD) is the largest co-ed professional law fraternity in the United States. Phi Alpha Delta has members who are university students, law school students, lawyers, judges, and politicians. It was founded in 1902 and today has over 300,000 initiated members. Approximately one out of six attorneys in the United States is a member of PAD. Five of the sitting Justices of the United States Supreme Court are members of PAD. From 1964 to 1968, Tom C. Clark, Associate Justice of the Supreme Court of the United States, served as Supreme Vice Justice of the Fraternity. Additionally, one of five of all Federal judges and three of ten of all State judges are PAD members. Six U.S. Presidents have likewise been members of PAD.