Lets take an example of "LOGIN APPLICATION".U r typing 
correct "USER ID" and "PASSWORD" and click "OK" button it 
is not going to the next page so this is a bug.This bug 
has "LOW SEVERITY" and "HIGH PRIORITY".If in the same 
example the systems crashes or hangs then we have to 
give "HIGH SEVERITY" and "HIGH PRIORITY".

The above answer is totally wrong.

user interface bugs     (Low sevirity)
        ex: Spelling Mistake   (High Priority)
        ex: Improper alignment (Low Proprity)

sevirity means defect with respective to Functionality
Priority means defect w    r          t  Customer 
requirement 

Partially i can accept with praveen

suppose take an example of client company NAME. in that if 
u have spelling mistake it is a LOW SEVIORITY coz there is 
no imapct on that Application,but in very strarting page 
have bugs means it is HIGH PRIORITY

SEVIORITY-how imapct on the appication is called seviority

PRIORITY-which bug should be fix first is called priority

Yes!!! as hary said the severity is some thing like intense 
affecting of the business functionality. Eg.: Missing of 
Logos in any of the screens.Its of low severity.

Priority is the developer's option that which bug is to be 
fixed first.

Spell mistakes are low severity bcoz it does not have 
impact on applicationbut will treated high priority at the 
time of presentation.

Login Window

Scenario: Provide valid user name and password and click on 
sumbit/login. A welcome message is wrongly displayed 
as "Welcom Peter"


Severity:It is a low severity since the bug doesn't effect 
the functionality of the login process.

Prioity : It is a high priority bug because an application 
shouldn't started with wrong impression.

Therefore the ratiois 1:3

In an Application when you click on "About Us" under "Help"
menu and suppose system gets hang then Priority is High and
Severity is Low. Because is the option where least users can
visit.

Sevirity--the bug how seviorly affecting the 
application /functionality. it is given by Tester

Priority--The bug which should be fix first based on 
severioty,it is given by Developer.

Example:-
if we you open google account,there if u seen "gogle" 
instead of "Google" (or) "google logo" has not be seen 
clearly
above two things are not affecting the functionality or 
testing process 
so testers give low sevirity.

But
developers will see the bug in customer point of view.it is 
very important for userinterface.so they will give High 
Priority.

if i am wrong mail me...,