What is a file handle? This is one of the various kinds of Tcl handles which is returned by Tcl commands such as open, [add other commands here that return this type of thing - perhaps relating to sockets, channels, other?]
They are a symbolic representation of an underlying operating system construct that represents an open input or output file/device. Examples:
set handle [open $filename w] puts $handle $line close $handle
The Tcl man pages use the term channel.