What does the explicit keyword mean in C++? When and why should it be used?

Hi everyone! I just started learning C++ and came across the `explicit` keyword. I understand that it is used before constructors, but I don't fully understand why it is needed and in what cases to use it. I have a simple class for working with a vector: ```cpp class Vector { public: Vector(int size) { data = new int[size]; sz = size; } private: int* data; int sz; }; ``` I can write code like this: ```cpp Vector v = 10; // Why does this work?! ``` The compiler compiles this without errors. But isn't `10` a number? Why does it suddenly turn into a Vector object? Is this some kind of implicit conversion? This seems dangerous to me, because I could accidentally pass a number where an object is expected, and the program will behave strangely.