Meanings of informal name in English

Can't we give it an informal name then, just between us?

The informal name "Sphinxian swamp siren" was already in use among the few informed parties.

The organization's informal name is English Heritage.

People have given them informal names inspired by their geographical peculiarities.

Those had informal names too: Queeds (Quarantine Enforcement and Detention), Feelies (Forward Intelligence), and Zerks (a contraction of Berserkers).