Below post will give you the details about the pick release status
Instance: 11i or R12
Table: WSH_DELIVERY_DETAILS
Column: RELEASED_STATUS
Possible Values:
B: Backordered- Line failed to be allocated in Inventory 
C: Shipped -Line has been shipped
D: Cancelled -Line is Cancelled
N: Not Ready for Release -Line is not ready to be released
R: Ready to Release: Line is ready to be released
S: Released to Warehouse: Line has been released to Inventory for processing
X: Not Applicable- Line is not applicable for Pick Release
Y: Staged- Line has been picked and staged by Inventory
C: Shipped -Line has been shipped
D: Cancelled -Line is Cancelled
N: Not Ready for Release -Line is not ready to be released
R: Ready to Release: Line is ready to be released
S: Released to Warehouse: Line has been released to Inventory for processing
X: Not Applicable- Line is not applicable for Pick Release
Y: Staged- Line has been picked and staged by Inventory
Delivery line statuses in detail
 Not Applicable (Code X)   
The delivery line can be invoiced but non-shippable, for example, a service line or a warranty line.
Not Ready for Release (Code N) 
 The
 delivery line is not eligible for pick release. This happens when the 
order line is manually imported into Oracle Shipping Execution using the
 Import Delivery Line concurrent process or the corresponding order line
 has not reached the Awaiting Shipping workflow activity.
Ready for Release (Code R)
  The delivery line is eligible for pick release.  Occurs
 when the order line has reached the Awaiting Shipping workflow activity
 (it is booked, scheduled, and in Oracle Shipping Execution).
Submitted to Warehouse (Code S)
Pick release has processed the delivery line and has:
1.       Created move order headers and lines.
2.       Found available quantity and created inventory allocations.
3.       Not
 pick confirmed. If you are using auto-pick confirm, it changes release 
status to Staged. If you are not using auto-pick confirm and want to 
progress the delivery lines, navigate to Oracle Inventory Move Order 
Transaction window and perform manual pick confirm.
Staged (Code Y)
 The delivery line is pick confirmed; inventory is transferred from storage sub-inventory to staging sub-inventory.  It remains staged until ship confirm.
 Backordered (Code B)
Some of the circumstances that can causes this status are listed below
Ø  Pick release has processed the delivery line and cannot find the entire quantity.  This
 typically occurs when the Oracle Inventory indicates that there is not 
enough material (either because there is not enough material or because 
the inventory balance is incorrect).   
Ø  At
 ship confirm, you: Enter Shipped Quantity that is less than Original 
Requested Quantity Backorder the entire delivery quantity transfer a 
reservation to cycle count.
Ø  This typically occurs when the material that you want to ship:
1.       Has become unavailable, for example, damaged, between picking and shipping.
2.       Is
 available and you backorder material for specific business reasons. For
 example, all available material has been allocated to a specific 
customer when you find out additional supply for other orders will be 
delayed.
  Shipped (Code C)
  The
 delivery line’s delivery is ship confirmed and posted as in-transit, OM
 Interface and Inventory Interface have processed, and the trip is 
closed.
  Cancelled (Code D)
  The order line that the delivery line supports is cancelled.