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.
The production possibility frontier curve or PPC is the diagrammatic representation of the different levels of production of two goods that can take place in an economy, ASSUMING all resources are fully and efficiently employed, no resource is equally efficient in the production of both goods and that resources are fixed.