A wet line is defined as:

A wet line is specifically identified as a water agent that is sprayed on the ground. This is utilized primarily in firefighting operations to create a barrier that helps to control or stop the spread of fire. By applying water directly to the ground, the wet line can help absorb heat, reduce fuel ignition potential, and provide a safeguard for firefighters as they work to contain the fire. It serves as an effective method for enhancing the safety of the operational area by creating a defined boundary that minimizes the fire's ability to advance.

Other definitions, while they may seem relevant in certain contexts, do not accurately describe a wet line. For instance, while one might think of a water line as simply a supply line for water, that does not capture the specific tactical application of a wet line in fire control situations. Similarly, a scratch line refers to a line created by digging or scraping away vegetation to expose mineral soil, which is a different technique for fire containment. A fire line refers generally to a constructed barrier that helps stop the spread of fire but does not specify the application of water that defines a wet line.