Update README.

Author: trekhleb

README.md

@@ -12,6 +12,11 @@ videos.
 
 ## Data Structures
 
+Data structure is a particular way of organizing and storing data in a computer so that it can 
+be accessed and modified efficiently. More precisely, a data structure is a collection of data 
+values, the relationships among them, and the functions or operations that can be applied to 
+the data.
+
 * [Linked List](https://github.com/trekhleb/javascript-algorithms/tree/master/src/data-structures/linked-list)
 * [Queue](https://github.com/trekhleb/javascript-algorithms/tree/master/src/data-structures/queue)
 * [Stack](https://github.com/trekhleb/javascript-algorithms/tree/master/src/data-structures/stack)