A non-negative function refers to any function that has values greater than or equal to zero for all points in its domain. It does not dip below zero on its graph.
Related terms
Positive Function: Similar to a non-negative function, this term refers to any function that has values strictly greater than zero for all points in its domain.
Increasing Function: This type of function always goes "upwards" from left to right on its graph without decreasing. It can include zero values as well.
Monotonic Function: A function that is either entirely increasing or decreasing (or both) over its entire domain.