Filters are used to manipulate the raw data from the simulation prior to rendering. The filter chain connects represents the manipulations that this data undergoes. Common filters include cut planes, clip planes, cut lines, etc. There is no limit to the length of the chain, but filter order matters in determining the result. For example, consider an isosurface filter, which produces surfaces that represent points of constant field values; and a threshold filter, which eliminates areas of the mesh where fields violate a specified lower and/or upper bound.
An isosurface filter followed by a threshold filter:
A threshold filter followed by an isosurface filter: