The loan balance describes the principal amount of a loan that is outstanding at any given point in time.
While a loan amount is the amount of funds that was initially borrowed from a lender, the loan balance is referred to at a certain time after the principal is reduced from the monthly payments.
For example, a loan amount was $100,000 a year ago and now the loan balance is $94,000. The reduction of $6,000 is due to the monthly installment which reduces the principal.