In this case, Bank transactions. Cat means a section of Category descriptions, Account means account descriptions, and so on. The D tag denotes the date. Fortunately the GnuCash QIF importer can handle all of the wacky date formats that the gnucash-devel list can find. If there are splits, the sum of all the split amounts is in a T field.
Money going out of the account is negative.
The M field is the transaction memo. The P field is the Payee. Note that nowhere in the transaction record, nor anywhere else in the file, does Quicken store the name of the account that the file describes. Don't ask me why not, I don't know either. In the Accounts Tab section there's a discussion of what we do with them.