Smoke testing is often referred to a point in development
where the programmer/engineer has deemed that section of
code or hardware ready So at that point it is superficially
tested before a full testing regiment is executed. This
phase is often done in software development where new builds
or versions are created often. This practice is very
important and time saving for the test group where the
developer/engineer is not in the same location.

somke test is nothing but checking the application is 
stable or not

Smoke tetsting is checking the major functionalty of the 
application working or not, before delivering to the client.

Smoke Testing is used to check basic functionality of the 
application

Smoke testing will be done before starting the functional 
Testing to ensure the system 'basically' works.