Hello,
Stereoelectronic effects are a way of explaining conformations, bond geometries, and reaction outcomes based on the electronic structure of a molecule.
The anomeric effect is an example of a stereoelectronic effect. Take glucose pentaacetate for example. Using sterics as a rational to predict the conformation results in the expectation that all substituents will be equaorial, and that that will be heavily favored. However, it is found that the substituent on the anomeric carbon carbon is favored to be axial.
I attached a ChemDraw document because pictures are probably going to be more helpful.