A virus refers to a microscopic particle, which can infect the biological organism's cells. Viruses possess the tendency to replicate themselves only by infecting a host cell, that is, within the cells, thus, it cannot multiply on their own.
At the most fundamental level, the viruses comprise genetic substance constituted within a protective protein coat known as a capsid. The prevalence of both the genetic substances and the presence of protein differentiates them from another virus like components like viroids and prions.
The structure in the image provided is of the womb of a pregnant woman. The major function of Structure X is to exchange materials between the mother and the fetus.