U

unbound:: adj. not having an associated denotation in a binding. See bound.
unbound variable:: n. a name that is syntactically plausible as the name of a variable but which is not bound in the variable namespace.
undefined function:: n. a name that is syntactically plausible as the name of a function but which is not bound in the function namespace.
unintern:: v.t. (a symbol in a package) to make the symbol not be present in that package. (The symbol might continue to be accessible by inheritance.)
uninterned:: adj. (of a symbol) not accessible in any package; i.e., not interned₁.
universal time:: n. time, represented as a non-negative integer number of seconds. Absolute universal time is measured as an offset from the beginning of the year 1900 (ignoring leap seconds). See Section 25.1.4.2 Universal Time.
unqualified method:: n. a method with no qualifiers.
unregistered package:: n. a package object that is not present in the package registry. An unregistered package has no name; i.e., its name is nil. See the function delete-package.
unsafe:: adj. (of code) not safe. (Note that, unless explicitly specified otherwise, if a particular kind of error checking is guaranteed only in a safe context, the same checking might or might not occur in that context if it were unsafe; describing a context as unsafe means that certain kinds of error checking are not reliably enabled but does not guarantee that error checking is definitely disabled.)
unsafe call:: n. a call that is not a safe call. For more detailed information, see Section 3.5.1.1 Safe and Unsafe Calls.
upgrade:: v.t. (a declared type to an actual type) 1. (when creating an array) to substitute an actual array element type for an expressed array element type when choosing an appropriately specialized array representation. See the function upgraded-array-element-type. 2. (when creating a complex) to substitute an actual complex part type for an expressed complex part type when choosing an appropriately specialized complex representation. See the function upgraded-complex-part-type.
upgraded array element type:: n. (of a type) a type that is a supertype of the type and that is used instead of the type whenever the type is used as an array element type for object creation or type discrimination. See Section 15.1.2.1 Array Upgrading.
upgraded complex part type:: n. (of a type) a type that is a supertype of the type and that is used instead of the type whenever the type is used as a complex part type for object creation or type discrimination. See the function upgraded-complex-part-type.
uppercase:: adj. (of a character) being among standard characters corresponding to the capital letters A through Z, or being some other implementation-defined character that is defined by the implementation to be uppercase. See Section 13.1.4.3 Characters With Case.
use:: v.t. (a package P₁) to inherit the external symbols of P₁. (If a package P₂ uses P₁, the external symbols of P₁ become internal symbols of P₂ unless they are explicitly exported.) The package cl-user uses the package cl.
use list:: n. (of a package) a (possibly empty) list associated with each package which determines what other packages are currently being used by that package.
user:: n. an active entity, typically a human, that invokes or interacts with a program at run time, but that is not necessarily a programmer.