Dual-ec-drgb is short for Dual Elliptic Curve Deterministic Random Bit Generator; a pseudorandom number generator based on the elliptic curve discrete logarithm problem.
It was standardized in NIST SP 800-90A, but Dual_EC has a pretty negative image. In 2006, Dual_EC was shown to be a slow and bad random number generator. By 2007, Shumow and Ferguson raised worries about the possibility of a backdoor in the specification. In 2013, The New York Times reported internal NSA memos suggest an RNG generated by the NSA which was used in the Dual_EC_DRBG standard does indeed contain a backdoor for the NSA.