What is Low end?
Low end refers to the bass region of a mix — roughly everything below 150–200 Hz, where the kick and bassline live. In techno, controlling the low end is the single most important mixing skill, because the genre's impact depends on it.
The rules of techno low end are strict because club systems are unforgiving: keep everything below ~100 Hz mono; give the kick's fundamental its own space and sidechain or EQ competing elements out of it; high-pass every channel that doesn't need bass; and decide deliberately how kick and rumble/bass share the spectrum — kick below, bass above, or interlocked rhythmically via sidechain. Check on a spectrum analyser but judge with ears and references: a great low end feels physical without being muddy.