The groundline is the main line used in fishing, to which shorter lines with hooks (called snoods) are attached. This setup allows the deployment of many hooks across a wide area, improving the chances of catching fish. The groundline is usually made from strong materials like nylon or monofilament and can extend for several kilometers. To make it easier to handle and more durable, the groundline is sometimes coated with tar or an oil mixture, which helps it resist wear and makes it easier to coil and store.

The groundline can be customized in length and thickness to suit different fishing situations, whether targeting fish like cod and haddock in shallow waters or deep-sea fish like Orange Roughy. The material and design of the groundline can also vary; for example, a mix of polyester and nylon sinks quickly and lasts longer, while polypropylene makes the line float.

Its dimensions and materials vary according to the usage, but it is usually made of twisted artificial fiber, either in polyester (terylene), polyamid (nylon) or polypropylene. Different types of fiber are often combined to provide special qualities. For instance, a groundline made from a mixture of polyester and polyamid sinks quickly and has good wear resistance, whereas one made from polypropylene floats. Groundlines are frequently impregnated with tar, or a mixture of oil and varnish, to increase their wear resistance and make the line easier to coil. (IS THIS STILL THE CASE?)