(idiomatic) The part of a tool or weapon that is physically used for its operation, rather than the part which is held.
The business end of a hammer is known as the "head".
(idiomatic,by extension) The part of anything that is most important and that produces the significant result.
2018 July 7, Phil McNulty, “Sweden 0-2 England”, in BBC Sport:
On this day, with expectation rising and the unmistakable feeling around this sweeping Samara Stadium that the World Cup is really reaching the business end, England delivered.