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.
Plumbing is a pretty broad category. Plumbers can do anything from fixing leaky faucets to installing sump pumps. They can repair or install your water heater or add a sink to your garage. They work everywhere in your home - kitchen, bathroom - wherever you need them.