Generally speaking "coupled aproach" refers to whether the autopilot is providing control deflections as commanded by a navigation source. This nav source can be a couple of things: you can have a ground based navaid provide the guidance as in the case of an ILS or VOR/DME or you can have an onboard system such as the FMS for a GNSS/RNAV approach. The "middleman" here is the flight director. As an example, for an RNAV approach you'd select the FMS as your data/nav source which would schedule your flight director displayed as command bars (chicken lips) and pseudo glideslope on your EFIS. You can handfly the approach from there if needs be or you could engage the autopilot - "couple-up".
LGC
