Tragically means in a way that is very sad, and it is most often used about death — especially a death that came early, suddenly, or by accident.

It has two jobs in a sentence. It can modify a verb: "he died tragically in a fire". More often it stands at the front and comments on the whole sentence: "Tragically, the letter arrived a day too late." In that second use the writer is not describing how something happened but telling you how to feel about it — the same slot as "sadly", "unfortunately", "luckily".

The word belongs to news reports and formal speech. "Three people tragically lost their lives" is newsreader language. In real conversation between friends, people say "it's so sad" or "it was terrible". Because journalists use it so heavily with death, the word now almost announces a death before the rest of the sentence arrives.

There is also a lighter, slightly funny use, where the thing is not sad at all: "tragically unfashionable", "tragically bad at singing". Here it just means embarrassingly, hopelessly. Young people use this more than old ones, and the tone is always joking. Though actually, mixing the two — using the light sense anywhere near a real death — lands very badly, so keep them apart.