I do not know how the definition is in other countries, but in Germany "active cases" are the number of cases still considered to be infectious.
Here in Germany, you do not need to be or feel ill but when you are still infectious, you are "an active case".
But I am still and always wondering a bit how and why our numbers are always at least a bit smaller than in other comparable countries.
OK, On the one hand, we have incredible many hospitals and many doctors, but this alone cannot be the reason.
On the other hand, this Covid-19-virus and its ability to mutate can surprise everyone in different ways in many countries.
The Omikron-Variant is now hitting again countries in Europe which were really successful up to now, e.g Portugal and Spain again.
And even China locks down again huge cities like Xi'an - which has ca. 13 million inhabitants - in a way which would be impossible in Europe - and it is NOT the Omikron-Variant there, it is still "Delta". The whole city of Xi'an is completely closed up, only one person in every household is permitted to leave the house to buy food and necessary goods and many other restrictions in Xi'an right now would look in Europe or in America like a city under martial law, but in China there are things possible you would not like to think about here in the West ....