var: It is a compile time entity
dynamic : it is a run time entity
var a = 5;
a = a+"abc";
Ans: compile time error, here a is integer datatype and trying to do addition operation with string datatype. so we cannot add integer with string
dynamic b = 5;
b = b+"abc";
Ans: at first b is a integer, then to do operation for adding with string, here dynamic will convert b integer data type to string data type then concatenate the both value.