An Internal table is a temporary table
that contains the records of an Advanced Business Application Programming
Program, while the program is being executed.
An internal table exists only during run time of a SAP program.
Internal table are used to process large volumes of data by using the ABAP language.
We must declare an internal table in an ABAP program when you need to retrieve data from database tables. Internal table can act as data type and data object.
A data type is the abstract description of data object an internal table is accessed
by using the concept of work area, a work area is a temporary memory space that
helps you in reading and modifying the data of an internal table line by line.