contra entry means the transaction from bank to cash and 
cash to bank in F4 in tally.

Contra entry refers to entry passed for the transaction 
which affects both bank & cash Ledgers and the entry should 
be posted to both cash and bank.

In Tally Contra Vouchers included only Ledgers related to 
Cash and Bank, & allowed enties related to bank and cash 
only eg: Transfer from 1 bank to another bank, Depositing 
to bank, withdrawing from bank, & transfering  of cash to 
petty cash.

contra means a single entry which effect both bank and cash 
in a same time .

contra entry is passed in following cases
1)when there is a transaction between two different banks 
i.e transfer of funds from one bank to another or,
2)cash withdrawn from bank or,
3)cash dedposited in bank or,

contra entry is only used in such type of transaction where 
only cash and bank item is affected.In tally F4 is used to 
post a contra entry.

contra entry means all bank transactions

Basicly Contra entry is transaction between cash and bank, 
but it also inclosed when two cosucutive entry are passed 
for nullyfi a particular entry with same amount,

contra entry means the entry which occurs both debit side 
and credit side in the three column cash book is called 
contra entry. 
 
 Gennerally entry occurs in three column cash book

In Oracle:

  Contra Entry Means GL Contra Entry and there below 
entries are passing.

          Funds in Transit Dr  xxxxxx ( Bank Account)

               To cash collection.

  This entry depends ib Fund in Transit and Cash in Transit.

Contra Entry occurs both side Dr and Cr.

Eg: Cash to Bank.

Dr               Cr

by cash        To bank

It is a bookkeeping entry that is entered on the opposite 
side of an earlier entry to cancel its effect on the 
account balance

It is better to say Contra is an adjustment entry, because 
it doesn't affect your Net Cash Balance.(whether cash in 
hand or bank, your current asset will be the same)

Where we recorded both the sides means debit and credit 
side is called contra. for example cash deposited into 
bank, cash withdraw from bank, cash transfer from one bank 
account to another bank account.