simple valid

http://postgis.net/docs/postgis_usage.html#OGC_Validity

geometries that are operated on are both simple and valid

a simple geometry is one that has no anomalous geometric points, such as self intersection or self tangency and primarily refers to 0 or 1-dimensional geometries (i.e. [MULTI]POINT, [MULTI]LINESTRING)

A POINT is inherently simple as a 0-dimensional geometry object.

MULTIPOINTs are simple if no two coordinates (POINTs) are equal (have identical coordinate values).

A LINESTRING is simple if it does not pass through the same POINT twice (except for the endpoints,
in which case it is referred to as a linear ring and additionally considered closed).

A MULTILINESTRING is simple only if all of its elements are simple and the only intersection between 
any two elements occurs at POINTs that are on the boundaries of both elements.

Geometry validity, on the other hand, primarily refers to 2-dimensional geometries (i.e. [MULTI]POLYGON) and defines the set of assertions that characterizes a valid polygon

By definition, a POLYGON is always simple. It is valid if no two rings in the boundary 
(made up of an exterior ring and interior rings) cross. The boundary of a POLYGON may intersect at a POINT
 but only as a tangent (i.e. not on a line). A POLYGON may not have cut lines or spikes and the interior rings 
must be contained entirely within the exterior ring.


A MULTIPOLYGON is valid if and only if all of its elements are valid and the interiors of no two elements intersect. 
The boundaries of any two elements may touch, but only at a finite number of POINTs.