A palace is the official residence of a head of state, head of church or dignitary, especially monarchical or imperial system of government. A palace is not as secure as a castle as it is not fortified against attacks. It is designed for leisure.
A castle is a large building that is fortified and contains many defenses such as thick walls, massive towers, and so on. Castles are often built of bricks or stone for strength. A nobleman or a king often inhabit it. They are created to fight battles and to withstand the attacks of enemies.
There are certain terms that people may use interchangeably such as castle and palace. It should be remembered that these two are not the same. A palace is known to be a residential place where the royal blooded or those who are considered to be important will reside.
The president of a country may reside in a palace but it does not mean that it is a castle. A lot of the palaces that you can find all over the world will not have the ability to ward off certain attacks. A castle is known to be very strong and it can be very large too. Its goal is to make sure that people will have enough protection from potential enemies who may try to take over the castle.