the.com/bivalence

means The principle that every proposition has exactly two possible truth values—true or false—with nothing in between.

from Built from Latin 'bi-' (two) plus 'valentia' (strength, worth, value), the same root that gives us 'valence' in chemistry for an atom's bonding capacity. Logicians borrowed that sense of 'value' to mean truth-value, so 'bivalence' literally means having exactly two of them. It belongs to a small family of logical terms—'multivalent,' 'many-valued logic'—that extend or challenge the two-valued assumption classical logic quietly relies on.