A Fluid is substance that can flow, like a Liquid or a Gas. The flow of a fluid can be represented by Streamlines, which are 'fluid elements' that move relative to each other.
In Laminar Flow, all the fluid elements flow in the same direction, and none of the streamlines cross over. It usually occurs at lower velocities and with streamlined objects. The word 'laminar' means flow in layers, and it is as if there are layers of fluid sliding over each other. In laminar flow, the 'layers' towards the middle tend to flow faster.
Turbulent Flow occurs at higher velocities or with non streamlined objects, when the flow lines become chaotic and mixed up. Eddies - small whirlpools - form where the flow gets mixed up.