Amortisation is another word for repayment of the mortgage. So amortisation means repaying the whole mortgage or part of it at regular intervals, with payment amounts remaining unchanged. In most cases, amortisation is annual or quarterly, depending on what has been agreed. Unlike the 1st mortgage, the 2nd mortgage is subject to an amortisation obligation: it needs to be amortised within 15 years or no later than the time you retire. If there are two borrowers, then the older applicant's age is used.
A distinction is made between direct and indirect amortisation.
Direct amortisation
With direct amortisation, you make regular repayments, as defined in advance, with the mortgage amount thereby reducing all the while. Thanks to the repayments, the annual interest liability also reduces automatically.