Internal tables are variable data objects in which you can store several values of identical type. This type has to be specified in the declaration and is called the row type of the internal table.
Each value occupies one row of the internal table. The number of rows is not restricted. Theoretically, you can store any number of values in one internal table. Limitations only come from technical boundaries like available memory or system configuration.
The initial value of an internal table is an empty table or, in other words, a table with 0 lines. There are different techniques for filling an internal table. The example uses the APPEND statement to add a new row at the end of the internal table and fill it with a value.
The type of an internal table is called a table type.
In the previous example we used TYPE TABLE OF in the DATA statement directly. The table type was bound to the declared variable.
As an alternative you can use TYPE TABLE OF in a TYPES statement to define a table type with a name. You can then use this table type, for example, in a DATA statement. The visibility of these types depends on the position of the TYPES statement.
There are also table types in the ABAP Dictionary. These table type are maintained with a dedicated editor. They are called global table types because they are visible anywhere in the system.