This is the 3440th most frequent Polish word.
zapalenie
Inflammation.
The word "zapalenie" is used here to mean "inflammation" or "infection" typically referring to medical conditions.
Zapalenie płuc to poważna choroba.
Pneumonia is a serious illness.
"Zapalenie" here denotes the act of igniting or lighting, particularly related to starting a fire.
Podczas pikniku, zapalenie ogniska było pierwszym krokiem.
During the picnic, lighting the campfire was the first step.
In this context, "zapalenie" refers to the action of lighting something like a candle.