Severity means the Impact of the Bug on the Applicaton

Priority is how urgernt the bug needs to be fixed

Severity can be High or Low
Priority can be High or Low

 
1]High Severity And Low Priority----If  there is an 
application , if that application crashes after mulple use 
of any functionality (exa--save Button use 200 times then 
that application will crash)

Means High Severity because application chrashed but Low 
Priority because no need to debug right now you can debug 
it after some days.

2]High Priority And Low Severity---- If any Web site 
say "Yahoo" now if the logo of site "Yahoo" spell s "Yho"  -
---Than Priority is high but severity is low.

Because it effect the name of site so important to do 
quick ---Priority

but it is not going to crash because of spell chage so 
severity low

severity is how badly the bug impact on the Application
Priority is selection to fix the bug  

Example:
suppose the bug is in the application name "Microsoft" 
to"Macrosoft" then the severity is low and the priority is 
high 
because:
while in these case the bug does not effect our application 
and our application function smoothly so the severiy is low 
but it make a high effect on company Name so the priority 
is High

severity means impact of the bug on the application.
priority means importance of the bug on the application.


Example:
suppose the bug is in the application name "Microsoft" 
to"Macrosoft" then the severity is low and the priority is 
high 
because:
while in these case the bug does not effect our application 
and our application function smoothly so the severiy is low 
but it make a high effect on company Name so the priority 
is High