The EXPLODE command allows you to change a grouped item into its individual elements so it can be edited. Putting it another way, The EXPLODE command breaks a compound object like a BLOCK up into its constituent parts (separate entities).
To explode an object
Do one of the following: 
Choose Explode from the Modify drop down menu. 
On a toolbar, click the Explode tool. 
Type EXPLODE in the command line and then press Enter.   
Select the entity, right click and select explode. 
A word of caution - if complex objects like hatching are exploded, the file size of the drawing may increase dramatically.
Ploylines can be exploded. A single polyline is then broken to its individual parts.

Explode command