Answer: It is a plane !
The picture on the left is the graph of the plane 2x + 3y + z = 6.

The red triangle is the portion of the plane when x, y, and z values are all positive. This plane
actually continues off in the negative direction. All that is pictured is the part of the plane that is intersected
by the positive axes (the negative axes have dashed lines).

Like systems of linear equations, the solution of a system of planes can be no solution, one solution or infinite solutions
.

No Solution of three variable systems , Case I

Below is a picture of three planes that have no solution. There is no single point at which all three planes intersect, therefore this system has no solution.

No Solution of three variable systems , Case II

The other common example of systems of three variables equations that have no solution is pictured below. In the case below, each plane intersects the other two planes. However, there is no single point at which all three planes meet. Therefore, the system of 3 variable equations below has no solution.

One Solution of three variable systems

If the three planes intersect as pictured below then the three variable system has 1 point in common, and a single solution represented by the black point below.

Infinite Solutions of three variable systems

If the three planes intersect as pictured below then the three variable system has a line of intersection and therefore an infinite number of solutions.