what is advanced sunrise and delayed sunset ?

This is due to the refraction of light coming from the sun.Because when light comes from the sun it generally travel from rarer medium to denser medium i.e., it travels from space[vaccum] to the earth's atmosphere[full of air]. 

Advanced sunrise:- it is due to that when the sun is below the horizon at that time the light from the sun enters to earth's atmosphere from space at get refracted away from the normal line of sun and it causes advanced sunrise.

Delayed sunset:- it is due to the reason that when the sun goes below the horizon at that time the sun's light pases from space to earth's atmosphere and it again get refracted from the normal line of the sun and it causes the delayed sunset.