idoc stands for intermediate documents,it is used for data
sending current system to remote system .
the structure of idocs is
1. data records
2. control records
3. status recors
          these are stored in sap tables like that.
edidd
edidc
edids

IDOC - Stands for Intermediate documents.
The purpose of the IDOC to carry the information from one 
system to the other system(Remote system)

For example : A delivery note trigger in the SAP should be 
udpated in the wearhouse system (Remote place). Which may 
be a non-sap system. 

When an idoc is triggered from SAP. The data of the 
delivery note will be carried in the Data Record 
(Structure/Segments),

From and to address will be there in the control record.

Status record holds the status (Once the remote system 
receives the IDOC) the status is updated in this area.

Idoc : Intermediate Document 

Exact use of it is transfering data from legacy system to 
the sap and vice versa.

Idoc structure is 
1 Data record : This data record can be one or more .
2 control record : This control record shd be one and it 
contain the info like who is the sender , who is the 
receiver , type of message etc.
3 Status record: This status records can also be one one or 
more basing upon the the stages the idoc is tranfered.
these status records are 1 to 75.
1 to 49 are reserved for outbound and 50 to 75 are reserved 
for outbound.

Idoc is a intermediate document.we can transfer the data 
across sap r/3 systems with idoc.idoc structure have three
components those are control record,data record,status 
record.Control record holds the adress details of inbound 
system.It has predefined structure EDIDC.Data record holds 
record in IDOC based on segments. predefined structure is 
EDIDD.STAUS shows the weather idoc sucees or not.It has
predefined structure BDIDOCSTAT.

Insimple words idoc is a container that carries data to be 
exchanged between sap system and the external sys which can 
be either r/3,r/2,legacy sys and structure of idoc is 
determined by the idoc type ..

IDoc (for intermediate document) is a standard data 
structure for electronic data interchange (EDI) between 
application programs written for the popular SAP business 
system or between an SAP application and an external 
program. IDocs serve as the vehicle for data transfer in 
SAP's Application Link Enabling (ALE) system.
Idoc structure is 
1 Data record : This data record can be one or more .
2 control record : This control record shd be one and it 
contain the info like who is the sender , who is the 
receiver , type of message etc.
3 Status record: This status records can also be one one or 
more basing upon the the stages the idoc is tranfered.
these status records are 1 to 75.
1 to 49 are reserved for outbound and 50 to 75 are reserved 
for outbound.

idoc is used to transfer data across applications.structure 
of the idoc is edidc,edidd,edids.