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. Ask for last month's actual figure rather than an estimate.
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 adds up over six months.