Jupyter Notebooks allow you to run Python, R, and other supported languages, through a web browser. The notebook consists of cells. Each cell can contain text in Markdown format and optionally Latex for math, or code. Code cells can be run out of order if desired and interactively adjusted; when run, their output is displayed below. The inclusion of text cells make it easy to include descriptions and analyses that go along with code cells and their output. Notebooks can be shared with others, making them a great way to share exploratory data analyses or example code.

(Credit: https://commons.wikimedia.org/wiki/File:IPython-notebook.png)