From Coastal Wiki
Definition of Abyssal plain:
The extensive, gently sloping or nearly level region of the ocean floor from about 2,000m to 6,000m depth.
This is the common definition for Abyssal plain, other definitions can be discussed in the article
The upper abyssal plain (2,000–4,000m) consists chiefly of graded terrigenous sediments known as turbidites.  It is sometimes also referred to as the continental rise.
- ↑ Pinet P.R. 1998.Invitation to Oceanography. Jones and Barlett Publishers. p. 508