A data lake is a system or repository of data stored in its natural/raw format, usually object blobs or files. Wikipedia

system or repository of data stored in its natural/raw format Wikidata

A massive, easily accessible data repository built on (relatively) inexpensive computer hardware for storing "big data". Unlike data marts, which are optimized for data analysis by storing only some attributes and dropping data below the level aggregation, a data lake is designed to retain all attributes, especially so when you do not yet know what the scope of data or its use will be. Wiktionary