Kaltmiete — cold rent — is the rent for the space and nothing else. Warmmiete is the Kaltmiete plus Nebenkosten: heating, water, rubbish collection, building maintenance, the caretaker. The gap is typically €80–200 a month for a Berlin flat, and rather more in an old building with bad windows and a cold winter.
German long-term ads usually quote the Kaltmiete, because that is the number the law works in — the deposit cap and most rent regulation are calculated on it. Short-let and sublet ads usually quote a single all-in figure, because the person leaving for three months just wants their outgoings covered. So the same word “rent” in two Berlin ads can mean two different things.
When a sublet ad quotes a number, assume it is all-in unless it says otherwise, then check. The question is one line: “is that warm, including Nebenkosten and electricity?” Electricity and internet are frequently not in the Nebenkosten even when everything else is, and on a short let they usually stay in the main tenant's name, so you are reimbursing rather than contracting.
The reason to be precise about it is that comparison shopping across a feed of listings is meaningless otherwise. A €700 cold room and a €700 warm room are perhaps a hundred euros a month apart, which over six months is a flight home.