The European Currency Unit was an electronic unit of account and not a full currency.
The Gibraltar ECU was named that way to differentiate it, as it is a separate currency.
While not explicitly named (at least not as clearly as I would like) the name we use seems the best option.
Created by the ‘Gibraltar Coinage (ECU) Act, 1990’ [LINK]
The two options appear to be…
[1] 3. Issue of Gibraltar ECU coinage
[2] diameter and weight of Gibraltar commemorative ECU coins.