Sperm penetration tests check to see whether a man's sperm can move through cervical mucus and the fallopian tubes to join with (fertilize) an egg. This test is usually done when a couple is having trouble becoming pregnant (infertility). There are different sperm penetration tests.
The idea that a boundary is shifting can be applied to different areas. A shifting frontier of science would be referring to the fact that science is always changing and growing, and always with new areas. In wartime, a shifting frontier would be an international border which is constantly being renegotiated.
Wiktionary(0.00 / 0 votes)Rate this definition: 1  shift(Noun) a type of women's undergarment, a slip. 2  shift(Noun) a change of workers, now specifically a set group of workers or period of working time. 3  shift(Noun) an act of shifting; a slight movement or change. 4  shift(Noun) the gear mechanism in a motor vehicle. 5  shift(Noun) a bit shift.