Internal tables are a standard data type object which exists
only during the runtime of the program. They are used to
perform table calculations on subsets of database tables and
for re-organising the contents of database tables according
to users need.

it is a temperary table ,which hold the data at run time 
only,it is 3 type
i.standard
ii.sorted
iii.hashed
it hold the data in two type of technique
i.with header line
ii.without header line

intermediate tables are called internal tables which exists 
only during the runtime of program. two types of internal 
tables are there,
1) internal table with header line
2) internal table without header line