Key concepts: separate clients matters are separate "accounts" within a trust account.  An IOLTA account is, by definition, a pooled trust account where a lawyer holds funds for multiple client matters.  The lawyer is required to keep track of funds for each client matter separately within the account.

A lawyer may be holding funds for several different client matters at the same time, but the lawyer should always be able to tell every single client how much of their money is in the account.  One example of a client matter is a real estate refinance.  A lawyer may handle half a dozen refinances in a month, some originating from the same lender.  Each refinance is a separate client matter for which the lawyer must maintain individual trust account records.

If a lawyer is keeping records in compliance with the rules of professional conduct and ALTA best practices, the lawyer will have a main register listing all transactions in the account and an individual client ledger for each client matter listing all transactions for that specific client.