Block periodisation concentrates training on one or two qualities for a few weeks at a time, instead of developing everything simultaneously. It was developed largely with elite athletes in mind.
Typical structure: an accumulation block (volume, aerobic base), a transmutation block (more specific, harder work), then a realisation block (taper and race-specific sharpening)
Blocks are often 2-6 weeks long
The concentrated load can give strong stimuli, but fatigue also concentrates
For amateurs with limited hours, a more mixed approach often works just as well; evidence comparing models in recreational athletes is limited
A mild version that works for many amateurs: a 3-week block with two VO2max sessions per week and the rest easy, followed by an easier week, then a block with two threshold sessions. You still run long every week, so the aerobic base is never neglected.