A Data Lake is a central repository from various data sources where the emphasis is put on storing data rapidly and for a low cost, at the expense of a well defined structure.

A wide variety of data can be stored in data lakes such as structured data (like columns and rows in classical RDBMS), semi-structured data (CSV, XML and JSON files), and unstructured data (images, videos, emails, web pages…).

In a Data Lake, the data is stored in a raw format, untouched, making it flexible for later usage. Data Lakes are, in general, a solid basis for data preparation, reports, visualization, in-depth analysis, data science and "machine learning".