dielectric polarization
When you apply an electric field across an insulator, no current flows through it — but something does happen inside. Every positive charge is nudged a little one way and every negative charge a little the other, so the material develops a lopsided arrangement of charge that points along the field, like a whole crowd that cannot leave the room but all lean toward the door. That gentle internal separation of charge is dielectric polarization, and it is the microscopic reason a dielectric raises capacitance.
Polarization P is the electric dipole moment per unit volume, and in ceramics it is built from three distinct mechanisms that act on very different timescales. Electronic polarization is the electron cloud of every atom shifting slightly against its nucleus; it is tiny but universal and so fast it still works at optical frequencies (about 10^15 hertz). Ionic polarization is the positive and negative ions of the lattice displacing in opposite directions — cations one way, anions the other; it is much larger in an ionic ceramic and keeps up to infrared frequencies (about 10^13 hertz). Dipolar or orientational polarization is permanent molecular or defect dipoles physically rotating to line up with the field; it is the largest but the sluggiest, and it fades out at lower frequencies. In a ferroelectric there is a fourth, giant contribution: whole regions of already-aligned dipoles (domains) whose walls sweep back and forth. The total epsilon_r is the sum of whatever mechanisms can keep pace with the applied frequency.
This is why the dielectric constant depends on frequency: as you raise the frequency, one mechanism after another can no longer follow the field and 'freezes out,' so epsilon_r steps down and, at each cutoff, a burst of loss appears. It also explains where the huge permittivity of the titanates comes from: in the perovskite structure a small, highly charged Ti4+ ion sits in a roomy oxygen cage and shifts far off-centre, giving an enormous ionic and dipolar polarization. Understanding which mechanism dominates, and how fast it responds, is how engineers design a ceramic for a stable low-loss microwave resonator versus a maximum-capacitance MLCC.
In barium titanate the Ti4+ ion sits about 0.1 angstrom off the centre of its oxygen octahedron. That tiny displacement, multiplied over every unit cell, is an ionic polarization so large it gives a dielectric constant in the thousands — thousands of times more charge stored than the electronic polarization of a simple oxide could provide.
Polarization is charge separation without charge flow: the atoms shift and rotate in place, and it is the sum of those shifts that a capacitor stores.
Polarization is not conduction. In a good dielectric the charges shift but do not travel through the material; if they did travel, that would be leakage current and dielectric loss, not useful storage.