A tag is a keyword or label that categorizes your question with other, similar questions. Using the right tags makes it easier for others to find and answer your question.
Questions about differential privacy, a measure and method for preserving privacy when querying statistical datasets.
Questions that address the challenges of storing data in digital form such that they remain accessible in the future.
Proof-of-work is a system where one can show an easily verifiable witness that they computed some amount of work, useful or not.