Scope is a context within which to resolve names to values.

Tcl has many scopes:

'''namespace''' is an hierarchal scope for resolving names of [commands] and variables.  The [variable] command references a variable name in namespace scope.

'''global''' scope is a distinguished namespace scope, equivalent to namespace :: in some interpreter

'''hidden''' scope is a per-interpreter scope for [interp] hidden commands

'''proc local''' scope is the context within which all otherwise unqualified variable names in a process are defined.

'''call frame''' scope is the context of some call frame in the current evaluation.  Proc local is a special case of a call frame scope, being the nearest enclosing call frame scope.

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In summary, there are two major kinds of scoping in tcl - dynamic and lexical (or static) scope.

'''dynamic''' scope is accessed by default inside a proc, or by means of [upvar] with unqualified names, and is preferred for variable name resolution.

'''static''' or '''lexical''' scope is accessed explicitly by namespace encoded names, the [global] operator, and implicitly by [command invocation] and by the [variable] operator.  Command resolution prefers dynamic scope.