It seems that it's a virtual term. It is not a bank account. It is the net result of gains-losses. And it seems that there are two types of such accounts – the llc's, and members'. The account should be recorded, but the record is not "the account", it is a record thereof.
Is this correct?
EDIT: (Since I got two answers referring me to Wikipedia.) I've seen the Wikipedia entry before posting my question. It tells us that this is included in something else and also the number of these. It does not tell us if this is a bank account or a file (whether paper or computer) or just a number.