A data structure is a collection of data that includes the structural relationships between the data.

If you didn't know what a data structure was, it is doubtful if this (or any other) definition would help much. So consider an everyday data structure: an ordered list. Here is a list of five numbers:

- 1
- 2
- 3
- 5
- 7

Each integer is
an item of data.
The *structure* is the order in which they are listed.
Each integer
is put in the correct place in relation to the other data.

An **ordered list** is a variety of **linear data structure**.
The structural relationship between the data is this:
Except for the first item and the last item,
each item in the list has one successor and one predecessor.
The first item in the list has one successor but no predecessor.
The last item in the list has one predecessor but no successor.

Is the following the same list as the one above?

- 2
- 7
- 3
- 1
- 5