LGR stands for Low-Grain Refrigerant. An LGR dehumidifier is the standard professional drying dehumidifier: it cools incoming air twice (pre-cooling it before the refrigeration coil), which lets it keep extracting water even when the air is already fairly dry — the exact condition in the later, hardest phase of a structural dry-down.
The 'grain' in the name is the unit: moisture in air is measured in grains per pound (GPP). Household dehumidifiers stall as grain depth drops; LGR units keep pulling, which is what gets materials from 'mostly dry' to verified dry-standard readings.
In a drying system, air movers evaporate moisture off wet materials and the LGR removes that moisture from the air, collecting it as condensate that drains away. For dense or cold conditions — crawl spaces, slabs, deep-saturated assemblies — crews may step up to desiccant dehumidifiers, which use a moisture-absorbing wheel instead of refrigeration and work in conditions that stall refrigerant units.
On estimates, dehumidifiers are per-unit, per-day line items sized to the cubic footage and moisture load of the space. Undersized dehumidification is the classic cause of dry-downs that drag on — one reason equipment lists on a professional scope aren't padding, they're physics.