I'm working towards making more of an official document for defining these fields, but I thought I would post what I have so far:

BasicTransaction Statuses

I don't think these statuses need any further explanation, but let me know if I'm mistaken.

• authorizedPendingCapture
• capturedPendingSettlement
• refundPendingSettlement
• settledSuccessfully
• refundSettledSuccessfully
• voided
• expired
• declined

Fraud Detection Suite (FDS or AFDS) Specific Responses

Both of these statuses indicate that a transaction is pending manual review by the merchant.

• FDSPendingReview
• FDSAuthorizedPendingReview

eCheck Specific Responses

• underReview - Under manual review, will be approved or declined.
• failedReview - Final status of a transaction that fails review.
• returnedItem - This will not show on an original transaction, but eCheck returns generate their own transactions with this status.

Other Errors

• communicationError - An individual transaction was rejected by the processor.  This is a final transaction status.
• settlementError - A day's batch was rejected by the processor.  This status is not final.  The merchant should try to recover the batch.
• General Error - This is a catch-all status for any transaction status that is not otherwise defined.

Transitional Transaction Statuses

These transaction statuses occur only as a transaction is taking place.  They should not be returned by the Transaction Details API.

• couldNotVoid
• approvedReview

Legacy Statuses

These transaction statuses relate to services that we have not offered for over 3 years.  Because an Authorize.Net merchant account stores only 2-3 years of history, you will not see these statuses actually returned in any normal operation.

• pendingFinalSettlement
• pendingSettlement
• updatingSettlement
• chargeback
• chargebackReversal
• authorizedPendingRelease