Horizontal Directional Drilling (HDD) is a trenchless method used to install underground utilities, such as water, gas, and telecommunications lines. This technique involves drilling a pilot hole along a predetermined path, which minimizes surface disruption and environmental impact. After the pilot hole is created, a larger reamer is pulled back through the hole to expand it. This allows for the installation of the utility pipe or cable. HDD is commonly used in urban areas where traditional excavation would be impractical or damaging to existing infrastructure.