(Pixel:
In digital imaging, a pixel (picture element) is the smallest unit of an image. Pixels are normally arranged in a regular 2-dimensional grid, and are represented by squares. The word pixel is based on the abbreviation "pix" for "pictures".
Flow:
A flow is the volume of a fluid which passes through a given surface per unit of time.
The term ‘fluid’ further expresses the quality of motion, to move or run smoothly with unbroken continuity, as in the manner characteristic of a fluid, or as to proceed steadily and easily.
Vector field:
Vector fields are used in physics to model and represent, for example, the speed and direction of a moving fluid through space, or the strength and direction of force, such as the magnetic or gravitational force, as it changes from point to point. A vector field is a construction in vector calculus which associates a vector to every point in a locally Euclidean space.)