Final answer:
The clearing made by bacteriophages on a bacterial lawn on an agar plate is known as a plaque, resulting from the lytic cycle of viral infection and cell lysis.
Step-by-step explanation:
The clearing made by bacteriophages in a "lawn" of bacteria on an agar plate is called a plaque. This clear area on a bacterial lawn is caused by viral lysis of host cells. When bacteriophages infect bacterial cells, they can enter a lytic cycle where the phage replicates and causes the cell to burst, releasing new phage particles that can infect neighboring cells. This cycle continues, leading to the formation of plaques, which are visible clearings as the bacteria are lysed. Each plaque originates from a single virus and can be used to estimate the number of virus particles in a sample, a process known as titering.