What is Painting ?

A painting is an image (artwork) created using pigments (color) on a surface (ground) such as paper or canvas. The pigment may be in a wet form, such as paint, or a dry form, such as pastels. Painting can also be a verb, the action of creating such an artwork.
Elements of Painting
Definition:
The elements of painting are the basic components or building blocks of a painting (and art generally). In Western art they are generally considered to be:
Color
Tone (or value)
Line (a narrow mark made by a brush, or a line created where two things meet)
Shape (2D, can be positive or negative) and Form (3D)
Space (or volume)
Texture (or pattern)
1.Color
Color is the most basic element of a painting. Every color has three aspects to it: hue or name, value or tone, and chroma or saturation. If you're trying to mix a color on your palette to accurately match a color in a subject, you need to consider all of these to get the "color right".
2.Tone (or value)
Tone is one of the basic elements of a painting and art. It refers to the lightness or darkness of a color, rather than what the actual color or hue is (e.g. cadmium red or Prussian blue).
What tone means in a painting context is simple. It's how light or dark a color is, rather than what the actual color or hue is. Yet implementing tone in a painting is often bothersome to artists because we get distracted by the strong appeal of color.
Every color can produce a variety of tones; how light or dark these are depends on the color. It's important to realize that tones are relative, that how dark or light they seem depends on what's going on around them. A tone that's obviously light in one context may seem darker in another if it's surrounded by even lighter tones.
Why is tone important? Here's what that master of color Henri Matisse had to say (in his A Painter's Notes, 1908): "When I have found the relationship of all the tones the result must be a living harmony of all the tones, a harmony not unlike that of a musical composition."
3.Line
Line encompasses everything from basic outlines and contours, to edges of tone and colour. Linework fixes the relationship between adjacent or remote elements and areas of the painting surface, and their relative activity or passivity.
Lines define and enclosed space. In drawing and painting a line represents many things such as and actual line, a person or a building. A line can be thick or thin; wavy, curved, or angular: continuous or broken; dotted dashed, or a combination of any of these.
4.Shape
A shape is created when a line is enclosed. Shape is one of the seven elements of art and it has a variety of uses in the creation of art.
A form is the three dimensional feel and look of an object. A shape looks flat and two dimensional. All objects have shape or form. Shapes and forms are both geometric.
Geometric shapes such as triangles, squares, circles have no volume and are two dimensional. Geometric forms have volume a word that describes the weight density and thickness of an object.
6.Space (or volume)
Space is the void between solid objects and shapes. It is everywhere and all around us. Everything takes up space in one form or another whether it’s two dimensional like drawing and painting, three dimensional like Sculpture and architecture.
7.Texture 
Texture is a general characteristic for a substance or a material. Texture exist all around us. It can be natural, invented, or manufactured. It can also be simulated or made to look and or feel rough, smooth, hard, or soft natural or artificial. Simulated textures such as a rough stone wall or a fluffy cloud are made to look and feel like real textures.
Sometimes these elements are also added to the list:
Composition
Direction (vertical, horizontal, angled)
Size
Time and movement (how the viewer perceives and looks at the painting)
Composition
Definition:
Composition is the term used for the arrangements of the elements in or the subject matter of a painting. Done successfully, it draws in the viewer and pulls their eye across the whole painting so that everything is taken in and finally settles on the main subject of the painting.
In his Notes of a Painter, Henri Matisse defined it this way: "Composition is the art of arranging in a decorative manner the diverse elements at the painter's command to express his feelings."
Direction 
(vertical, horizontal, angled)
Size
Definition:
Size is added to paper during manufacturing to make it more or less absorbent. The less size there is in a sheet of paper, the more it will absorb the paint.
Size is also the term used for a glue (sometimes made from rabbit skin) put on a canvas before priming to protect it from the oil in oil paint. It's also used to seal wood panels before painting and on plaster, if you don't want the paint to seep into the plaster.
Lastly, size can also mean the physical dimensions of a sheet of paper