A combustion wave (flame) propagating in the unreacted medium at a velocity that is less than the speed of sound as measured at the flame front, and which propagates via a process of heat transfer and species diffusion across the flame front. The flame front is not coupled in time nor space with the preceding weak shock front. The pressure peak coincides with the flame front but a marked pressure rise precedes it. Typical maximum pressure ratios generated by deflagrations in confined volumes are in the range of 8-12. Maximum propagation velocities of 10-100 m/s are typical, although up to several hundred m/s may be observed.