The F
pilus is also known as a
conjugation bridge. It's a long, narrow structure which protrudes from the surface of the "
male"
bacterium and connects the "
male" to the "
female"
bacterium during the process of
bacterial conjugation, which occurs when
genetic material in the form of the F
plasmid is swapped between two bacterial
cells.
In other words, it's roughly the microbial equivalent of a penis.
From the science dictionary at http://biotech.icmb.utexas.edu/