Type select if the same type, i.e both Raster Items, Text frames, Paths etc
Fill Color select if the fill color is the same
Stroke Color select if the stroke color is the same
Stroke Width select if the stroke width is the same
Opacity select if the Opacity is the same
Number of Anchors select if the number of anchor points is the same
Size within select if the size of the shape is the same size as the currently selected shape, plus or minus the set tolerance
Area within select is the area of the shape is within the set tolerance for the currently selected shape. Note that this is using Illustrators built in area calculation and may not match the exact area of the shape depending on path directions. For example, two shapes with the same visual area may not match if the paths are drawn in different directions or are compound paths.
Search in
Entire Document Search the entire document
Same Artboard Only search for matching shapes on the same Artboard as the selected shape
Same Layer Only search for matching shapes on the same layer as the selected shape