Testing Basic functionality. It is a first test on built.

If you have a login screen, you have to just enter whatever
required and check whether it works fine.

Typically an initial testing effort to determine if a new 
software version is performing well enough to accept it for 
a major testing effort.

After getting the initial build from developers we have to
test the stability of the build & whether we can continue
for further testing.

It is the type of testing in which one can perform an
initial and overall testing in order to check whether
everything is proper with respect to the application(The
availability  of
features,objects,functionalities,connectivies.......etc) so
that a detailed testing can be performed successfully.

what DEEPA said that is absolutly correct. Smoke test is 
nogthing but checking for the  availability of all the 
features of an application. Both Sanity and Smoke are 
alomost same.....

It is a type of initial, shortspan and non detailed 
testing. In which one can check the availability of all the 
features of an application . So that detailed testing can 
be performed .

It is the initial testing,after getting the build from the 
developer,testers will conduct smoke testing to check the 
main functionalities of the application.Smoke testing is 
nothing but Sanity testing.