What is slack byte?

What is slack byte?
Ans:
To store any type of data in structure there is minimum fixed byte which must be reserved by memory. This minimum byte is known as word boundary. Word boundary depends upon machine. TURBO C is based on 8086 microprocessor which has two byte word boundary. So any data type reserves at least two byte space.
Suppose a structure word1:

struct word1
{
char a;
int b;
char c;
};