Axiom is  a general purpose Computer Algebra system. It is useful for research and development of mathematical algorithms. It defines a strongly typed, mathematically correct type hierarchy. It has a programming language and a built-in compiler.
Polybutylene is simply a type of plumbing material that was manufactured between the late 70's and early 90's. It is thought that it was installed in over 6 million homes during that time period.
A plumb bob is a very simple tool that features a small weight and a string. When the string is suspended at the top with the weight at the bottom, the weight will straighten the string to establish a perfectly plumb line that can be used for reference when installing building materials in a plumb orientation.