A highlighter is a felt-tip pen filled with transparent fluorescent ink. The first highlighter was introduced in 1963 by Carter's Ink Company, using the trademarked name Hi-Liter. Avery Dennison Corporation now owns the brand, having acquired Carter's Ink Company in 1975.
Many highlighters come in bright, often fluorescent colours. Being fluorescent, highlighter ink glows under black light. The most common colour for highlighters is yellow, but they are also found in pink, blue, green, orange, and purple varieties. Red highlighters can be purchased along with a green translucent sheet used to hide the highlighted material. This product is sold in Japan and some other countries, and can also be bought online. Some yellow highlighters may look greenish in colour to the naked eye.Yellow is the preferred color to use when making a photocopy as it will not produce a shadow on the copy.
Highlighters are available in multiple forms, including some that have a retractable felt tip or an eraser on the end opposite the felt. Other types of highlighters include the trilighter, a triangularly-shaped pen with a different-coloured tip at each corner, and ones that are stackable. There are also some forms of highlighters that have a wax-like quality similar to an oil pastel.
'Dry highlighters'(occasionally called dry line highlighters) have, an applicator that applies a thin strip of highlighter tape (physically similar to audio tape) instead of a felt tip. Unlike standard highlighters, they are easily erasable. They are different than dry mark highlighters, which are sometimes advertised as being useful for highlighting books with thin pages.
Other uses 
- Some word processing software can simulate highlighting by using a technique similar to reverse video on some terminals. Similar to this is the program Web Highlighter, which allows users to "...attach highlighting, notes, and links to any Web page viewed with Microsoft Internet Explorer 4.0 or later."
This is what highlighting on a modern word processor looks like: Example text.
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- WO 2005042654, Schmid, Christian; John L. Stoffel & Bill Sperry, "Ink compositions for use in highlighter markers and associated methods", published 12 May 2005
- Hilary, Greenbaum; Rubinstein, Dana (2012-01-20). "WHO MADE THAT? The Hand-Held Highlighter". The New York Times Sunday Magazine. pp. MM20. Retrieved 2012-01-26.
- Highlighter Ink Glowing Under a Black Light
- Web Highlighting