A lacuna is an empty space in the law with no regulations applicable or an absent part in a law or another written document such as a contract. In other words, it denotes an instance when there is no controlling law or contractual provision. The plural is lacunae. More common in UK than US English, lacuna is synonymous with loophole or a technicality, often unintentional, which an entity can exploit to avoid the scope of a law or a contractual provision without directly violating the law or breaching the contract.
“The question of dual citizenship is a legal lacunae in some jurisdictions.”