That is a socket for a 194 light bulb.
When the parking lamps are on, and you open the frunk, that bulb is supposed to help you pack/unpack your baggage at night.
Near the relays is supposed to be a sheetmetal bracket with a cutout where that socket can fit into, to hold the bulb socket securely, rather than having it dangle around.
Looks like your Fiero doesn't have the bracket installed. I don't know if they came standard on all cars. You can get a bracket though from a junkyard Fiero.
[This message has been edited by pmbrunelle (edited 08-01-2020).]