marker

A marker is a writing instrument or device used to apply marks to a surface. In everyday use, markers refer to pen-like tools that deposit ink through a porous tip to label, draw, or highlight on materials such as paper, plastic, wood, or fabric.

Common categories include permanent markers, which use solvent-based ink that adheres to many surfaces; dry-erase markers, which use erasable ink suitable for nonporous boards; and highlighters, which employ fluorescent inks designed to emphasize text. Marker tips come in various shapes, such as bullet, fine, and chisel, influencing line width and application. Ink formulations range from solvent- and alcohol-based to water-based, affecting durability, odor, cleaning, and potential bleed-through on thin media.

Other specialized types include paint markers for nonporous or outdoor surfaces, fabric or textile markers for clothing and crafts, and industrial markers intended for construction or labeling on tough substrates. Proper care involves keeping the cap on when not in use, storing markers upright, and testing on a inconspicuous area to prevent staining or damage to the surface.

In biology and medicine, marker has a broader meaning. A genetic marker is a DNA sequence with a known location used in mapping or identifying individuals or traits. Biomarkers are measurable indicators of a biological state or condition. In computing and navigation, markers are reference points or objects used to designate positions, such as map markers or bookmarks. The term broadly denotes anything used to mark, designate, or identify.