What's differences between costs and expenses and which expenses could called costs and which not ?

A cost might be an expense or it might be an asset. An expense is a cost that has expired or was necessary in order to earn revenues

cost usually used to obtain the assets that used to generate the revenues but expenses charges through the operation of getting the revenue it self 

cost to be amortized over the assets life term 

while expenses to be direct  charged when it realized 

costs has a long effect and balances transferable from period to another

Expenses is limited to the period incurred 

Every cost is called an expense but not every expense is called cost...

Direct material is cost it must be an expense

Building is an asset it can be called an expense but can not called a cost