What is strong-typing versus weak-typing? Which is preferred? Why?

In weak typing, it is allowed to define a block of memory as another type (casting).
Languages like C, C++ are weakly and statically typed.
Languages like Perl and PHP are weakly typed as you can add numbers to strings and they will implicitly coerce it.

Languages like Java, C# and Python are strongly typed. In these the type conversion needs to be explicitly handled.

For scripts we use weak typing.

In big programs, we use strong typing which can reduce errors at compile time