A data lake is a massive, easily accessible, centralized repository of large volumes of structured and unstructured data.
Techopedia explains Data Lake
The data lake architecture is a store-everything approach to big data. Data are not classified when they are stored in the repository, as the value of the data is not clear at the outset. As a result, data preparation is eliminated. A data lake is thus less structured compared to a conventional data warehouse. When the data are accessed, only then are they classified, organized or analyzed.
Hadoop, an open-source framework for processing and analyzing big data, can be used to sift through the data in the repository.