What do you mean by ozone hole? What are its consequences?

In polar regions,stratospheric clouds provide the surface for chlorine nitrate and hypochlorous acid,which react further to give molecular chlorine. Molecular chlorine and $HOCl$ are photolysed to give chlorine-free radicals.
$ClONO_{2(g)} + H_2O_{(g)} \to HOCl_{(g)} + HNO_{3(g)}$
$ClONO_{2(g)} + HCl_{(g)} \to Cl_{2(g)} + HNO_{3(g)}$
$HOCl_{(g)} \xrightarrow{hv} \dot{O}H_{(g)} + \dot{Cl}_{(g)}$
$Cl_{2(g)} \xrightarrow{hv} \dot{Cl}_{(g)} + \dot{Cl}_{(g)}$
The chlorine-free radicals lead to the decomposition of ozone as:
$\dot{Cl}_{(g)} + O_{3(g)} \to Cl\dot{O}_{(g)} + O_{2(g)}$
Hence,a chain reaction is initiated. The chlorine-free radical is continuously regenerated,thereby depleting the ozone layer. This phenomenon is known as the 'ozone hole'.
Effects of depletion of the ozone layer:
The ozone layer protects the Earth from the harmful $UV$ radiations of the sun. With the depletion of the layer,more radiation enters the Earth's atmosphere. $UV$ radiations are harmful because they lead to the ageing of skin,cataracts,skin cancer,and sunburns. They cause the death of many phytoplanktons,which leads to a decrease in fish productivity. Excess exposure may even cause mutations in plants.
An increase in $UV$ radiations decreases the moisture content of the soil and damages both plants and fibers.