Open-ended structures give investors a claim on the fund's assets at net-asset-value rather than at whatever price another buyer will pay. Most mutual funds and ETFs are open-ended.
The structure creates a liquidity mismatch wherever the fund's holdings are less liquid than the redemption terms it offers. A daily-dealing fund holding corporate bonds, property or small caps promises liquidity it does not have when everyone asks at once. Several property funds have suspended dealing for exactly this reason.
Tools used to manage that mismatch include swing pricing, redemption notice periods, cash buffers and in extreme cases suspension. Read the dealing terms before assuming daily liquidity is guaranteed. See closed-end-fund and interval-fund for structures that handle it differently.
Related: mutual-fund, closed-end-fund, interval-fund, net-asset-value, liquidity, redemption-gate