Founded in 2018, 50by40 is an organisation with the mission to achieve

A 50% reduction in the global production and consumption of farmed animal products by 2040, with the remaining production systems being environmentally and socially sustainable, regenerative and humane, achieved via a Just Transition of the farming system.

This question asks specifically about global meat production. Our World In Data claims global meat production in 2018 was 342.42 million tons, a 46.68% increase since 2000. A 50% reduction from this level would result in global meat production declining to 171.21 million tons, a level last seen in 1988.