TAPEFILE gives the name for the tape initialization file. See Section 3.4 for content details. The alternative is to have the tape initialization details imbedded in the SCHED input following TAPEINI or to use the defaults which are fine for the VLBA.
Note that a tape initialization file is almost certainly NOT needed. Most parameters in it relate to initial tape head and pass positions which no longer make sense in the disk era. The one possibly useful parameter is the media specification, but that should be defined in the station catalog and would only be used during periods of transition.
Under unix, environment variables may be used.