  Understanding how electronic structure determines the reactivity of solid
surface, is a central topic of modern surface science. This is mostly commonly
done through some intermediate quantity termed descriptor. However, such
descriptors are very scarce for solid surface compared to for molecule, likely
due to their significantly more complex electronic structure (cf. molecules).
Here we elaborate on the theory of a concept dubbed "Fermi softness", which
distinguishes itself by enabling prediction of surface reactivity with spatial
as well as atomic resolution. Other pertinent concepts and descriptors are also
mentioned so as to make the treatment comprehensive.
