Nostro account
A nostro account is a bank account one bank opens at another bank, usually to facilitate foreign currency transactions and so on. It is necessarily a cash account, and necessarily a proprietary asset of the depositing bank. It is not a client money account.
Nostro seems to be a fun word to say. It sounds technical, and you should expect people in ops to throw it around carelessly, often in connection with a client money offering. To be clear, a “client nostro” account is like a “Tall Dwarf”. It is a contradiction in terms.
Odd spot: The “Tall Dwarfs” were an alternative pop band in New Zealand in the 1980s. According to Wikipedia they still exist, though most likely only in the minds of their progenitors — musical luminaries who probably thought Tall Dwarfs was a clever, and not tiresome name. Assiduous fans might be able to name a tune or two, but would be hard pressed to hum one.