Some of Tcl's documentation refers to ''procedure''s
as a distinct type of command.

A ''procedure'' is a Tcl command that is created
by the [proc] command.

For example the [info args] command expects its
argument to be the name of a procedure.  Names 
of other commands passed to [info args] will
cause an error to be raised.

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Some languages (e.g. [Pascal]) uses the terms "function" and "procedure" to denote subroutines which do and don't respectively return a value. In Tcl, the distinction is quite different: a ''function'' is a subroutine available in [expr]essions (and as of Tcl 8.5 these are merely implemented by commands in the [tcl::mathfunc] namespace). A ''procedure'' is a command created by [proc], and like any other command it returns a value. In the absence of an explicit [return], this value is simply the value returned by the last command in the procedure body.

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see also [Pass by reference] and [Implicit upvar].

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