Diarrhoea

According to NICE, 3 or more loose or liquid stools in a day (or more frequently than is normal for the individual) counts as diarrhoea.

Persisting for more than 14 days makes it chronic.

Acute typically gastroenteritis. Presence of blood and/or mucus suggests more invasive inflammation, viz colitis.

In kids, can occur with pretty much any illness!

Vomiting with diarrhoea makes a primary gut cause more likely, but still not specific.