I am moving to the US soon ! What is the difference between a lease and a sub-lease ?

A lease is a new contract you sign for an apartment. In a sub-lease you take over somebody else's existing lease. A sub-lease can benefit you because it would be for less than a year.

Joe & Barbara see an apartment -- sign the 12 month lease -- they are the lessee and the owner is the lessor.

Joe or Barbara change jobs -- they need to move -- they find a new person to rent the apartment - Jane Doe -they have sublet the apartment to Jane Doe. Jane is responsible to pay the rent for the remainder of the lease. If Jane defaults in the rent and stops paying, Joe and Barbara may be asked to pay the balance.

A lease is between landlord and tenant.

A sub-lease is between tenant and someone he turns the apartment over to. He moves out and you move in (with approval of the landlord).