According to the definition on the Mermaid site, Mermaid is a JavaScript based diagramming and charting tool that renders Markdown-inspired text definitions to create and modify diagrams dynamically. In short, when creating online Markdown-based documentation or publications, like with GitHub or with static site generators that use Markdown to generate content, you can move from static images to dynamically generated diagrams. Mermaid currently supports diagrams such as flowcharts, sequence diagrams, class diagrams, ER diagrams and Gantt charts with more diagrams being added.