The AllocGrp component conveys the details of each account when a trade (or block trade) is allocated into one or more accounts.
Additional detail from the official source
This repeating group is optionally used for messages with AllocStatus(87) = 0 (accepted) or 2 (account level reject) to provide details of the individual accounts that were accepted or rejected. In the case of a reject, the reasons for the rejection should be specified. This group should not be populated where AllocStatus(87) has any other value.
This is a reusable definition. Requiredness is relative to this structure; its use and conditions in a message remain on that message's page. Version links browse the other dictionary, not an assumed equivalent component.
May specify the broker of credit if ProcessCode(81) is step-out or soft-dollar step-out and Institution does not wish to disclose individual account breakdowns to the executing broker.
Allocation identifier assigned by the Firm submitting the allocation for an individual allocation instruction (as opposed to the overall message level identifier).
AvgPx for this AllocAccount. For F/X orders, should be the "all-in" rate (spot rate adjusted for forward points) for this allocation, expressed in terms of Currency(15). For Fixed Income always express value as "percent of par".