DFHEIBLK(Data facility Heirarchy Exec Interface BLocK) is a cobol copy book which will be automatically included by the cics translator in all the cics programs. This will contain PIC clauses of all the fields that are mandatory in any cics program.
Ex: transid will be stored in EIBTRNID(which is a field) , The time at which the trransaction has started would be stored in EIBDATE and EIBTIME. the cics service you are requesting for.. like SEND or RECEIVE will be stored in EIBFNID.....and so on..
You better go thru the APPENDIX C of the CICS hand book written by Kageyama. All the fields are listed out there.
If i am wrong at any point, correction would be appreciated.