Ada LRM - Index U

Unary adding operator 4.4 (4.4), 4.5 (4.5), C (C); 4.5.4 (4.5.4)
  [see also: arithmetic operator, overloading of an operator, predefined
  operator]
     as an operation of a discrete type 3.5.5 (3.5.5)
     in a simple expression 4.4 (4.4)
     overloaded 6.7 (6.7) 

Unary operator 4.5 (4.5); 3.5.5 (3.5.5). 3.5.8 (3.5.8), 3.5.10 (3.5.10), 3.6.2 (3.6.2),  4.5.4 (4.5.4), 4.5.6 (4.5.6), C (C)
  [see also: highest precedence operator, unary adding operator]
        as an operation of a fixed point type 3.5.1 (3.5.1) 4 (4)

UNCHECKED_CONVERSION (predefined generic library function) 13.10.2 (13.10.2); C (C), 13.10 (13.10)

UNCHECKED_DEALLOCATION (predefined generic library procedure) 13.10.1 (13.10.1); 4.8 (4.8),
   C (C), 13.1 (13.1) 4 (4)

Unconditional termination of a task
  [see: abnormal task, abort statement] 

Unconstrained array definition 3.6 (3.6) 

Unconstrained array type 3.6 (3.6)
     as an actual to a formal private type 12.3.2 (12.3.2)
     formal parameter 6.2 (6.2)
     subject to a length clause 13.2 (13.2) 

Unconstrained subtype 3.3 (3.3), 3.3.2 (3.3.2)
  [see also: constrained subtype, constraint, subtype, type]
     indication in a generic unit 12.3.2 (12.3.2) 

Unconstrained type 3.3 (3.3); 3.2.1 (3.2.1), 3.6 (3.6), 3.6.1 (3.6.1), 3.7 (3.7), 3.7.2 (3.7.2)
     formal parameter 6.2 (6.2)
     with discriminants 6.4.1 (6.4.1), 12.3.2 (12.3.2) 
                                     
Unconstrained variable 3.3 (3.3), 3.6 (3.6), 3.7 (3.7); 12.3.1 (12.3.1)
     as a subcomponent [see: subcomponent] 

Undefined value
     of a scalar parameter 6.2 (6.2)
     of a scalar variable 3.2.1 (3.2.1)

Underline character 2.1 (2.1)
     in a based literal 2.4.2 (2.4.2)
     in a decimal literal 2.4.1 (2.4.1)
     in an identifier 2.3 (2.3) 

Unhandled exception 11.4.1 (11.4.1)

Unit
  [see: compilation unit, generic unit, library
        unit, program unit, storage unit, task unit] 

Universal expression 4.10 (4.10)
     assigned 5.2 (5.2)
     in an attribute designator 4.1.4 (4.1.4)
     of a real type implicitly converted 4.5.7 (4.5.7)
     that is static 4.10 (4.10)

Universal type 4.10 (4.10)
  [see also: conversion, implicit conversion]
     expression [see: expression, numeric literal]
     of a named number 3.2.2 (3.2.2); 3.2 (3.2)
     result of an attribute [see: attribute] 

UNIVERSAL_FIXED (predefined type) 3.5.9 (3.5.9)
     result of fixed point multiplying operators 4.5.5 (4.5.5)

UNIVERSAL_INTEGER (predefined type) 3.5.4 (3.5.4), 4.10 (4.10); C (C)
  [see also: integer literal]
     argument to a conversion 3.3.3 (3.3.3), 4.6 (4.6)
     attribute 3.5.5 (3.5.5), 13.7.1 (13.7.1), 13.7.2 (13.7.2), 13.7.3 (13.7.3); 9.9 (9.9)
     bounds of a discrete range 3.6.1 (3.6.1)
     bounds of a loop parameter 5.5 (5.5)
     codes representing enumeration type values 13.3 (13.3)
     converted to an integer type 3.5.5 (3.5.5)
     of integer literals 2.4 (2.4), 4.2 (4.2)
     result of an operation 4.10 (4.10); 4.5 (4.5)    

UNIVERSAL_REAL (predefined type) 3.5.6 (3.5.6), 4.10 (4.10)
  [see also: real literal]
     argument to a conversion 3.3.3 (3.3.3), 4.6 (4.6)
     attribute 13.7.1 (13.7.1)
     converted to a fixed point type 3.5.10 (3.5.10)
     converted to a floating point type 3.5.8 (3.5.8)
     of real literals 2.4 (2.4), 4.2 (4.2)
     result of an operation 4.10 (4.10); 4.5 (4.5) 

Updating the value of an object 6.2 (6.2) 

Upper bound
  [see: bound, last attribute] 

Upper case letter 2.1 (2.1)
  [see also: basic graphic character]
     A (A) to F (F) in a based literal 2.4.2 (2.4.2)
     E (E) in a decimal literal 2.4.1 (2.4.1)
     in an identifier 2.3 (2.3) 

Urgency of a task 
  [see: task priority]

Use clause (to achieve direct visibility) 8.4 (8.4); 8.3 (8.3), D (D)
  [see also: context clause]
     as a basic declarative item 3.9 (3.9)
     as a later declarative item 3.9 (3.9)
     in a code procedure body 13.8 (13.8)
     in a context clause of a compilation unit 10.1.1 (10.1.1)
     in a context clause of a subunit 10.2 (10.2)
     inserted by the environment 10.4 (10.4) 

USE_ERROR (input-output exception) 14.4 (14.4); 14.2.1 (14.2.1), 14.2.3 (14.2.3), 14.2.5 (14.2.5), 14.3.3 (14.3.3),
14.3.10 (14.3.10), 14.5 (14.5)