An annuity is a fixed payment for a set period of time (usually monthly). The amount is the same over the term of the annuity. An annuity consists of two parts. The first is the principal payment (mortgage), which is the amount the borrower has borrowed. The second is the interest payment, which is the lender’s remuneration for lending the money.
For consumer loans, the annuity payments are the same for the life of the loan, whereas for mortgages, the annuity is contractually fixed for the duration of the interest rate fixation. You can see the proportion of interest for each instalment in the repayment schedule you have with your loan agreement.
Source: www.moneta.cz, www.kb.cz, www.remaxalfa.cz