2021 Edition
Jupyter notebooks are great tools allowing you to develop highly readable and easy to understand code in Python. It is mostly used when creating proof of concepts where you want to be able to merge code snippets together with comments, images, graphs, LaTeX equations etc.
Jupyter notebooks are divided into cells. Each cell can be a code cell or a text cell (well, actually there are also two other types, but it's not important for now). Code cells let you add executable Python code to them and text cells are places where you can add all description you need. Code cells can be executed one by one or all at once (i.e. one after the other automatically). Each cell can also be rerun without rerunning whole notebook - it is very useful when you want to, for example, rewrite a function responsible for creating statistics, without retraining the whole neural network model, which could take a lot of time. You can find more detailed info about Jupyter Notebooks here.
Google Colaboratory, or “Colab” for short, is a product from Google Research. Colab allows anybody to write and execute arbitrary python code through the browser, and is especially well suited to machine learning, data analysis and education. More technically, Colab is a hosted Jupyter notebook service that requires no setup to use, while providing free access to computing resources including GPUs and TPUs. See more in this video.
Each of the notebooks on this repository contains a link at the top, which redirects you to Colab where you can run and experiment with the notebook without having to worry about installing Jupyter or any other software.