any of a number of similar colours evoked by light consisting predominantly of the longest wavelengths discernible by the human eye, in the wavelength range of roughly 630–740 nm. Longer wavelengths just past this range are called infrared (below red) and cannot be seen by the naked eye although they can be sensed as heat. In some cultures, certain shades of red are used to symbolise anger or aggression. It is the colour of blood when exposed to sunlight. In western countries, it is most commonly referred to as a colour of evil, love, and sometimes, though rarely, happiness.
The word red comes from the Old English rēad. The word can be further traced to the Proto-Germanic rauthaz and the Proto-Indo European root reudh-. In Sanskrit, the word rudhira means red or blood. In the English language, the word red is associated with the colour of blood, certain flowers (e.g., roses), and ripe fruits (e.g., apples, cherries). Fire is also strongly connected, as is the sun and the sky at sunset. After the rise of socialism in the mid-19th century, red was used to symbolise and describe revolutionary movements.