Local charge can cost energy
Mott emphasized that moving an electron between nearly localized ions can require a substantial Coulomb energy. An independent-electron band count may then predict conduction where correlated electrons instead resist charge rearrangement.
This line of reasoning emerged in the 1930s and developed alongside work on disordered and amorphous materials. The 1977 award recognizes that broader electronic-structure contribution.
An interaction gap differs from a mobility edge
A correlation-induced charge gap concerns the energy needed to change occupations. A mobility edge separates localized from extended states in an energy spectrum. An insulator can involve either mechanism or a combination, so the term insulating does not identify the cause.
Hopping has a different temperature signature
Localized electrons can conduct at finite temperature by phonon-assisted hopping. The preferred hop balances distance against the energy difference between sites. A stretched-exponential temperature law needs its dimensionality, density-of-states assumptions and competing processes checked before interpretation.
Sources: [2]
The disorder Lab supplies one comparison
The existing coherent disorder model illustrates localization without electron–electron interactions. It cannot generate a Mott charge gap. Reading the two articles together makes the distinction explicit, instead of assigning the same animation to every poorly conducting material.