Analysis of information sources in references of the Wikipedia article "QED vacuum" in English language version.
For each stationary classical background field there is a ground state of the associated quantized field. This is the vacuum for that background.
The interaction will last for a certain duration Δt. This implies that the amplitude for the total energy involved in the interaction is spread over a range of energies ΔE.
Thus in QED the presence of an electric charge eo polarizes the "vacuum" and the charge that is observed at a large distance differs from eo and is given by e = eo/ε with ε the dielectric constant of the vacuum.
We use three distinct notions of vacuum in quantum gravity