Monofilament fishing line (shortened to just mono) is fishing line made from a single fiber of plastic material, as opposed to multifilament or braided fishing lines constructed from multiple strands of fibers. Most fishing lines are now nylon monofilament because they are cheap to manufacture and can be produced in a range of diameters which have different tensile strengths (called "tests" after the process of tensile testing, or possibly as a portmanteau of "tensile" and "strength"). Monofilament line is also available in different colors, such as clear, white, green, blue, red, and fluorescent.
Monofilament is made by melting and mixing polymers and then extruding the mixture through tiny holes, forming strands of line, which is then spun into spools of various thicknesses. The extrusion process controls not only the thickness of the line but its test as well.