Tableau like other BI tools has a range of products:

• Tableau Desktop: Desktop product is used to create OPTIMIZED QUERIES out from pictures of data. Once the queries are ready, you can perform those queries without the need to code. Tableau desktop encompasses data from various sources into its data engine and creates an interactive DASHBOARD. 
• Tableau Server: When you have published dashboards USING Tableau Desktop, Tableau servers help in sharing them throughout the organization. It is an enterprise-level feature that is installed on a Windows or Linux server. 
• Tableau Reader: Tableau Reader is a free feature available on Desktop that lets you open and views data visualizations. You can filter or drill down the data but restricts editing any formulas or performing any kind of actions on it. It is also used to extract connection files. 
• Tableau Online: Tableau online is also a paid feature but doesn’t need exclusive installation. It comes with the software and is used to share the published dashboards ANYWHERE and everywhere. 
• Tableau Public: Tableau public is yet another free feature to view your data visualizations by saving them as worksheets or workbooks on Tableau Server.