Answer:
The term which is used to define an initial amount of money that is borrowed or invested is:
Principal amount
Explanation:
Principal amount--
It is the amount or sum of money that is borrowed or invested for some purpose.
In context of borrowing a person borrows this amount and at the time of repaying his loan he has to pay this amount and the extra amount is to be paid which is the interest on the loan.
Similarly in context of investment a principal amount is to be invested and then the interest is gained on the amount.