Adjacency Relation
The Set 
of Edges of a Graph 
, being a set ofunordered pairs of elements of 
, constitutes a Relation on . Formally, an adjacency relation is any Relation which is Irreflexive and Symmetric.
- Univariate Function
- Univariate Polynomial
- Universal Graph
- Universal Statement
- Universal Turing Machine
- Unknot
- Unknotting Number
- Unless
- Unlesss
- Unmixed
- Unpoke Move
- Unsafe
- Unsolved Problem
- Unstable Improper Node
- Unstable Node
- Unstable Spiral Point
- Unstable Star
- Untouchable Number
- U-Number
- Upper Bound
- Upper Integral
- Upper Limit
- Upper Sum
- Upper-Trimmed Subsequence
- Upward Drawing