PENIS is an acronym for Proton Enhanced
Nuclear Induction Spectroscopy.
In layman's terms this is a method of determining which light wavelengths a given substance will absorb, or what wavelengths it emits. This is useful in determining the exact makeup of a substance.
The story behind this acronym is that the editors of a scientific journal back in the 1970s did not like a certain scientists idea on something or another (rejecting his paper). So a few months later he submitted a wonderful paper on Proton Enhanced Nuclear Induction Spectroscopy, and he referred to it by its acronym PENIS throughout the entire paper (they still published it). The article appeared in the Journal of Magnetic Resonance (probably not a lot of subscribers to that one), in 1974, and was written by T Merrick.