I   want  to  know  that  what  is  the  'difference'  between 
"equity  loan  and  letter  of  credit" ??

It would help to know the nature/context in which you are asking this.

But I'd guess that you are in a situation that you need to guarantee
that you are able to make payment.

In an "equity loan" you would offer up something that has value to
guarantee payment.  For example, your home (assuming you have equity
in your home, meaning it is worth more than what you owe).

A letter of credit would be a document that your bank would provide
that guarantees that they are willing to loan you a specific amount of
money.