What is "yellow flag"

Quarantine \Quar"an*tine\, n. [F. quarantaine, OF. quaranteine, fr. F. quarante forty, L. quadraginta, akin to quattuor four, and E. four: cf. It. quarantina, quarentine. See Four, and cf. Quadragesima.]

1. A space of forty days; -- used of Lent.

2. Specifically, the term, originally of forty days, during which a ship arriving in port, and suspected of being infected a malignant contagious disease, is obliged to forbear all intercourse with the shore; hence, such restraint or inhibition of intercourse; also, the place where infected or prohibited vessels are stationed.

   Note: Quarantine is now applied also to any forced stoppage of travel or communication on account of malignant contagious disease, on land as well as by sea.

3. (Eng. Law) The period of forty days during which the widow had the privilege of remaining in the mansion house of which her husband died seized.

   Quarantine flag, a yellow flag hoisted at the fore of a vessel or hung from a building, to give warning of an infectious disease; -- called also the yellow jack, and yellow flag.

n. A Eurasian and northwest-African aquatic iris, ''Iris pseudacorus''.

n. common yellow-flowered iris of Europe and North Africa, naturalized in United States and often cultivated [syn: yellow iris, yellow water flag, Iris pseudacorus]

Yellow flag may refer to:

• Iris pseudacorus, an aquatic flowering plant
• A flag of a yellow colour:
  • Yellow flag (contagion) historically displayed on ships to indicate the presence of disease or quarantine (obsolete)
  • Racing flags used in motor sports to indicate hazardous conditions
  • Penalty flag used in various sports including American football
• Green-Yellow Flag Line transport on the Chao Phraya River north of Bangkok

In International maritime signal flags, plain yellow, green, and even black flags have been used to symbolize disease in both ships and ports, with the color yellow having a longer historical precedent, as a color of marking for houses of infection, previous to its use as a maritime marking color for disease.

The present flag used for the purpose is the "Lima" (L) flag, which is a mixture of yellow and black flags previously used. It is sometimes called the "yellow jack", which became a name for yellow fever. Cholera ships also used a yellow flag.

The plain yellow flag ("Quebec" or Q in international maritime signal flags), perhaps derives its letter symbol for its initial use in quarantine, but this flag in modern times indicates the opposite—a ship that declares itself free of quarantinable disease, and requests boarding and inspection by Port State Control to allow the grant of "free pratique".