Liquidity describes how quickly something you own can be turned into spendable money without a meaningful loss in value.
Cash in a current account is perfectly liquid. Property is not: selling takes months and carries large transaction costs. Investments sit in between — often sellable within days, but at whatever price the market offers that week, which may be a bad one. This is why liquidity, not return, is the deciding property for emergency money: an asset that is worth a lot but cannot be accessed in time solves nothing.