Here-be-dragons Definition

phrase

A fanciful notation, commonly attributed to historical maps, held to indicate either the belief that unknown dangers exist in a certain location on the map, or that actual dragons can be found there.

Wiktionary

By extension, used to indicate that which is unknown or uncertain, particularly if it seems to carry some type of risk.

Wiktionary

Origin of Here-be-dragons

Evidence of the use of this term as a notation on actual historical maps is lacking. The only known appearance of an equivalent phrase in any language on a historical map is of Latin HC SVNT DRACONES (“here are dragons”), placed on the east coast of Asia, on the Hunt-Lenox Globe, which dates from c. 1510.

From Wiktionary