My US bank showed a transaction without a check number and called it an "inclearing check". The month is not over, so i haven't seen how it's shown on a statement. But a bit of searching on the web shows that it seems to be a common term, yet I'm dissatisfied with the answers found on the web.
An "inclearing check" is a check on your account that the bank has received in either paper or automated form from the bank at which it was presented for cashing or deposit. Usually this terminology is reserved for actual checks, because the "inclearing" process is part of the traditional way banks handle checks. However, it can also apply to ACH tranfer requests, which are the electronic "digest" of your check produced by the depositing bank to speed the transfer of funds, and are also how most companies process "automated payments" when you give them a bank account number. An automated payment doesn't require an actual check number and the company often doesn't provide one (so that the automated check has little to no chance of being confused with a paper one you wrote).
Many banks simply list transactions like these as "processing" or "pending", which may also apply to transactions made in other ways such as with a debit card.