Marines & Regular Army – the difference?

To all the learned experts on military matters and ex & current serving officers

How do the Marines (of any country) differ from the regular army (of any country). What are the G.F.R (general functionary roles) of the Marines and how do these GFRs differ from the GFRs of other services and their commandos?

Any member of this forum with valid & learned knowledge on these points – pls offer your opinions.
NOTE – NO FLAMERS pls between Army & Marines.. (the Americans fall for this usually).

Cheers
Dandpatta