Even before Edison was born, scientists had experimented with making light bulbs. These bulbs burned out after a few minutes. What Edison invented was the first incandescent light that was practical, that would light for hours and hours. He and his muckers also had to invent hundreds of other parts to make the light bulbs in your home work. Light switches, electric meters, wiring--all these had to be invented too.
The pip command is a tool for installing and managing Python packages, such as those found in the Python Package Index. It's a replacement for easy_install.
Logically, a Requirements file is just a list of pip install arguments placed in a file. Note that you should not rely on the items in the file being installed by pip in any particular order. Requirements files are used to hold the result from pip freeze for the purpose of achieving repeatable installations. In this case, your requirement file contains a pinned version of everything that was installed when pip freeze was run. pip freeze > requirements.txt pip install -r requirements.txt.