Definition:Null


 * Set Theory:
 * Null Set
 * Null Relation


 * Abstract Algebra:
 * Null Ring
 * Null Module


 * Measure Theory:
 * Null Measure


 * Analysis:
 * Null Sequence


 * Mathematical Logic:
 * Null URM Program


 * Polynomial Theory:
 * Null Polynomial


 * Graph Theory:
 * Null Graph


 * Formal Systems:
 * Null String


 * Linear Algebra:
 * Null Space


 * Ideal Theory:
 * Null Ideal


 * Category Theory:
 * Null Object

Also see

 * Definition:Zero
 * Definition:Trivial
 * Definition:Empty