Full Idea
In a 'supervaluation' we take a trivalent interpretation, and assign to each wff T (or F) if it is T (or F) in every precisification, leaving the third truth-value in any other cases. The wffs are then 'supertrue' or 'superfalse' in the interpretation.
Clarification
See Idea 13692 for 'precisification'
Gist of Idea
A 'supervaluation' assigns further Ts and Fs, if they have been assigned in every precisification
Source
Theodore Sider (Logic for Philosophy [2010], 3.4.5)
Book Reference
Sider,Theodore: 'Logic for Philosophy' [OUP 2010], p.83
A Reaction
[my non-symbolic summary] Sider says the Ts and Fs in the precisifications are assigned 'in any way you like', so supervaluation is a purely formal idea, not a technique for eliminating vagueness.
Related Idea
Idea 13692 A 'precisification' of a trivalent interpretation reduces it to a bivalent interpretation [Sider]