Short for norovirus. A highly contagious virus that causes acute gastroenteritis, especially common in winter; frequently used in speech and news.
学級でノロが流行して、数日間休校になった。
Norovirus spread through the class, and school was closed for several days.
ノロに感染しないように、手洗いと消毒を徹底してください。
To avoid norovirus infection, be sure to wash hands and disinfect thoroughly.
病院では『ノロの疑いあり』と表示されていた。
The hospital had a sign saying 'suspected norovirus.'