YO: A Chareidi is simply a Jew who follows Judaism as the Torah meant it, in full without looking for compromises.
In other words, a default practicing Jew.
The name was given to them by outsiders; they didn’t assume it for themselves. Much like Orthodox, another term imposed by outsiders who broke off from normative Judaism default Judaism and gave a name to those who simply continued following the Torah like their ancestors.
300 years ago those called this today would’ve simply been called Jewish.