We show that a broadly accepted criterion of laser-induced breakdown in solids, defining the laserbreakdown threshold in terms of the laser fluence or laser intensity needed to generate a certain fraction of the critical electron density rc within the laser pulse, fails in the case of high-intensity fewcycle laser pulses. Such laser pulses can give rise to subcycle oscillations of electron density ρ with peak ρ values well above ρ c even when the total energy of the laser pulse is too low to induce a laser damage of material. The central idea of our approach is that, instead of the ρ = ρ c ratio, the laser-breakdown threshold connects to the total laser energy coupled to the electron subsystem and subsequently transferred to the crystal lattice. With this approach, as we show in this work, predictions of the physical model start to converge to the available experimental data.Laser-induced breakdown of solid materials has been a subject of in-depth research since the invention of lasers 1,2 . In the era of rapidly progressing laser sources of extremely short and broadband optical field waveforms 3,4 , understanding the regimes and scenarios of laser-induced breakdown, as well as the available parameter space for a reversible photoionization-assisted control of optical properties of solids is central for emerging petahertz optoelectronic technologies 5,6 , nonlinear-optical bioimaging 7,8 , short-pulse laser surgery 9,10 , laser micromachining 11 , and compression of high-peak-power ultrashort laser pulses in transparent solids [12][13][14] . Systematic experimental studies of optical breakdown and laser-induced damage, performed within more than five decades, have revealed distinctly different physical scenarios of optical breakdown induced by laser pulses of broadly varying intensities, fluences, and pulse widths [15][16][17] . These studies helped identify a broad range of physical processes contributing to laser-induced breakdown 18 , including field-induced and avalanche ionization, nonlinear dynamics of a laser beam, plasma effects, radiation absorption by impurity and defect states, as well as collisional dynamics, diffusion, and recombination of free carriers 9 . While the specific regime of laser-induced breakdown can depend on all the above-listed factors, ionization dynamics and the related buildup of free-carrier density always play a central role in laser breakdown, providing a mechanism whereby the laser field is coupled to a material. This fact is recognized by a broadly accepted criterion of laser-induced breakdown 9,18-25 that defines the laser breakdown threshold in terms of the laser fluence or laser intensity needed to generate a certain fraction of the critical electron density within the laser pulse. This criterion has proven to be useful in a broad range of pulse widths, offering a powerful tool for the analysis of a laser breakdown by pico-and femtosecond light pulses and helping understand a variety of related laser-matter interaction phenomena in a broad class of solid materials and syste...