Incipient Metals: materials that exhibit a unique mechanism between covalent and metallic bonding. Data for a diverse set of 58 materials show that metavalent bonding is not just a superposition of covalent and metallic cases, but instead gives rise to a unique and anomalous set of physical properties.

Ref: Wuttig M , Deringer V L , Gonze X , et al. Incipient Metals: Functional Materials with a Unique Bonding Mechanism[J]. Advanced Materials, 2017, 30(51).