FileNameJoin

FileNameJoin[{name1,name2,…}] joins the namei together into a file name suitable for your current operating system. 

FileNameJoin[{CloudObject[…],name2,…}] joins the namei to the path in the specified cloud object. 

FileNameJoin[{LocalObject[…],name2,…}] joins the namei to the path in the specified local object.

FileNameJoin[name1,name2, …] is equivalent to FileNameJoin[{name1,name2,…}].

Please visit the official Wolfram Language Reference for more details and examples on core symbols.