driver is a replacement of unfinished main component.

stub is a replacement of unfinished sub components.

driver is used in Botton-up approach.

stub is used in Top-down approach.

Driver is a simulation(sample) for calling program ,it is
used in Bottom-up Approach

Stub is a simulation for called program ,it is used in
Top-Bottom Approach

TTopdown & bottom up approch is included in Integration 
testing..
Topdown approch: to test Main module to 
submodule ..sometimes the main module is till not developed 
the temparary  module isdeveloped and tested this temparay 
module name is called stub.Its acts like submodule
Bottom up apporch :
Bottom up approch:to test submodule to main module...
    Some times submodule is still not developed the the 
temporary module is developed i,e called driver .It act as 
main module

Driver and stub is used in integration testing.

Driver is used in bottom up approach of integration 
testing.driver calls the function to be tested. 

Stub is used in top down approach of integration 
testing.stub is called by the function to be tested.It is a 
piece of code which stimulates the activity of other module 
in system.

E.g. System consist of modules A,B and C.
Development of module A and B is done.Now we cant afford to 
wait till the time module C is ready.In this case we can 
develop dummy of module c which will stimulate the activity 
of module c in system and we can continue with our 
integration testing.Here dummy of module C is stub.When we 
will connect all three modules to ensure they function 
properly then it is called as driver.