Fundamental physical constant ɛ0 = 1/(µ0.c02) exactly, where µ 0 is the permeability of vacuum and c0 the speed of light in vacuum. It is equal to 8.854187817... x 10E-12 F m-1.
Sources:
CODATA 2006 (https://doi.org/10.1103/RevModPhys.80.633)
Green Book, 2nd ed., p. 14 (https://goldbook.iupac.org/files/pdf/green_book_2ed.pdf)