Off-plan
Buying off-plan means signing a contract and paying for a property that has not been built yet, usually in instalments tied to construction stages. You are buying a contract and a set of drawings, not a building.
Also called: pre-construction, pre-selling, off-the-plan
Developers sell off-plan because it funds the build: your instalments pay for the concrete that becomes your apartment. Buyers do it because off-plan prices are lower than finished stock and because in the fastest-moving markets the good units are gone before completion.
The trade is straightforward once stated plainly. You accept two risks the finished-property buyer does not: that the building is delivered late, and that what is delivered differs from what the contract described. In exchange you pay less and you get first choice.
The mechanism that makes this bearable is the payment schedule, and it deserves more attention than most buyers give it. Payments are either tied to construction milestones (foundation complete, structure complete) or simply to calendar dates. The first kind gives you a reason to ask whether the stage was really reached. The second gives you none: the date arrives, the invoice arrives, and whether anything was built that month is not contractually your business.
Foreign buyers carry a third risk on top: distance. The developer's word is the only source of information about a building on another continent, and the developer is the party being paid.
Read your payment schedule before you read anything else in the contract. Whether payments follow stages or dates decides how much say you have if the build falls behind.