In Verilog declaration of data/task/function within modules are specific to the module only. They can't be shared between two modules. Agreed, we can ACHIEVE the same via cross module referencing or by including the files, both of which are known to be not a great solution.

The package construct of SystemVerilog aims in solving the above issue. It allows having global data/task/function declaration which can be used across modules. It can contain module/class/function/task/constraints/covergroup and many more declarations (for complete list please refer section 18.2 of SV LRM 3.1a)

The content inside the package can be ACCESSED using EITHER scope resolution operator (::), or using import (with option of referencing PARTICULAR or all content of the package). 

01.package ABC;
02.// Some typedef
03.typedef enum {RED, GREEN, YELLOW} COLOR;
04. 
05.// Some function
06.void function do_nothing()
07....
08.endfunction : do_nothing
09. 
10.// You can have many different declarations here
11.endpackage : ABC
12. 
13.// How to use them
14.import ABC::Color; // Just import Color
15.import ABC::*; // Import everything inside the package

In Verilog declaration of data/task/function within modules are specific to the module only. They can't be shared between two modules. Agreed, we can achieve the same via cross module referencing or by including the files, both of which are known to be not a great solution.

The package construct of SystemVerilog aims in solving the above issue. It allows having global data/task/function declaration which can be used across modules. It can contain module/class/function/task/constraints/covergroup and many more declarations (for complete list please refer section 18.2 of SV LRM 3.1a)

The content inside the package can be accessed using either scope resolution operator (::), or using import (with option of referencing particular or all content of the package). 

01.package ABC;
02.// Some typedef
03.typedef enum {RED, GREEN, YELLOW} Color;
04. 
05.// Some function
06.void function do_nothing()
07....
08.endfunction : do_nothing
09. 
10.// You can have many different declarations here
11.endpackage : ABC
12. 
13.// How to use them
14.import ABC::Color; // Just import Color
15.import ABC::*; // Import everything inside the package