These are a common form of investment policy. Regular premiums are paid, and when the term of the endowment expires a lump sum is paid out. The lump sum may be used to repay a mortgage, for example, although to achieve this the investment performance needs to be sufficient to build up the required capital and this performance cannot be guaranteed.
Most endowments have a protection element such that if the policyholder should die then a lump sum becomes payable.
THE VALUE OF INVESTMENTS AND THE INCOME FROM THEM MAY GO DOWN. YOU MAY NOT GET BACK THE ORIGINAL AMOUNT INVESTED.