The motion is a very important concept to be studied in physics. It can be expressed in either of things distance and displacement. Distance and displacement seems to be same but are not so!. Let us take any body moving how much path it covers in quantitatively decides its distance. How far it goes from initial point tells about its displacement. Lets study more about this..

A man leaves his home from point A. He moves 3m north and reaches point B, 5m in the west to reach point C. Then 3m in the south to reach point D and finally 3m to east and comes the same initial point A. Here the path traveled is 3 + 5 + 3 + 5 = 16m. Here path traveled is distance which is 16 m. But the man is in the same point where he was initially hence his displacement is zero.....
Lets us have more clear idea about the concept using these points:
Lets us have more clear idea about the concept using these points:
Distance 
Displacement 

1  It is path taken by the body when it is moving (actual path)  It is the shortest distance between the initial point to the point where body has reached finally. 
2  It is a scalar quantity  It is a vector quantity 
3  It is always positive  It can be any thing  positive, negative or zero. 
4  It is always greater than or equal to displacement  It can never be greater than distance traveled. 
Yes it can be negative. We know that Displacement always takes place in a particular direction and hence is a vector quantity.
A negative displacement does not mean that the body speed has decreased but is moving in opposite direction to direction specified.
A negative displacement does not mean that the body speed has decreased but is moving in opposite direction to direction specified.
The displacement from A to B is positive (+ 5 m) and from B to A is negative ( 5 m).
No distance can never be negative. As a body is in motion its distance goes on increasing what ever might be path chosen irrespective of direction. Hence it can never be negative.
In the above figure distance from A to B is 5 m and B to A is 5m. Total distance traveled is 10 m.
In the above figure distance from A to B is 5 m and B to A is 5m. Total distance traveled is 10 m.
Speed is that which tells how fast a body moves!. It can be positive or zero but can never be negative. Distance traveled depends on speed. The speed in particular direction gives the velocity. It may be positive, negative or zero. The velocity decides what will be the displacement.