My friend has a 2012 Honda Civic and the license plate light cover falls off. I searched online for replacement and I can’t find the official term for it. Does anyone know?
If you are talking about the piece which has the Honda emblem in it, the only thing I'm seeing it called is Trim (garnish) assembly, trunk lid.
It would be part "27" or "28" on the right hand side.
A quick search using The Google with the terms "2012 Honda Civic license plate light cover" returns a number of results. At the top of the list is the PartsGeek.com option for under four dollars US.
I'm not sure why, but it references the passenger side in the description. More than one location?
It took a bit of snooping around because strangely, for the 4 door sedan model, the trim piece isn't under the Trunk Lid category. Instead it was under Electrical > License Light, labelled as Garnish Assy., RR. License.
Annoyingly, there are different part numbers for every paint colour, so I linked the parent page that contains all of them. Basically, you're looking for 74890-TR3-A01Z_, where the last digit specifies the paint colour. It's labelled as part #5 in the diagram. Note that 74890-TR0-A01Z_ parts are manufactured in Japan, so they're most likely intended for the JDM/international Civic models. You can consult with your dealer to confirm the exact part number, although from my experience, they usually take a while to figure it out from their diagrams.
I believe the part number actually contains all of the clips and the emblem as well (the ones encapsulated by the hexagon-ish shape for #5), which may or may not be what you want. In these cases, there is no way to specify just the trim piece itself from Honda's parts system.