What are internal tables? How do you get the number of lines in an internal table?

i)It is 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.
ii)using SY-DBCNT.
iii)The number of memory allocations the system need to allocate for the next record population.