This is the difference between the statement ending balance and the G/L system balance, less outstanding checks (debits entered in Sage 50 but not included on the statement) and including deposits in transit (credits entered in Sage 50 but not included on the statement).
When all transactions listed on the bank statement are entered and cleared in Sage 50 and outstanding transactions have been accounted for, the unreconciled difference should be zero (0.00). If not, check the bank statement to make sure that each transaction listed is also entered in Sage 50. For example, a service charge listed on the statement may need to be entered in Sage 50. You may need to check with the bank or make an adjusting entry.