Horizontal Directional Drilling (HDD) is a trenchless technique used to install underground pipelines, conduits, or cables without digging large trenches. It involves drilling a steerable pilot hole, then enlarging it using a reamer to create a path for the pipe. Drilling fluids stabilize the bore and transport debris. Finally, the pipe is pulled back through the hole. HDD is widely used for crossing under obstacles like rivers or roads, minimizing surface disruption and environmental impact. It’s commonly employed in industries like telecommunications, oil and gas, and utilities, offering cost-effective, efficient installation in complex or sensitive terrains.