Terminology
An element of an ideal I is said to be I-null or I-negligible, or simply null or negligible if the ideal I is understood from context. If I is an ideal on X, then a subset of X is said to be I-positive (or just positive) if it is not an element of I. The collection of all I-positive subsets of X is denoted I+.
Read more about this topic: Ideal (set Theory)