References a namespace.using NamespaceName; The using statement specified in a source file allows referencing classes, entities and functions declared in the namespace without specifying the namespace name every time. Its behavior is fully equivalent to the using statement in C#. E.g. the following 4 code snippets are equivalent:

entity Test
{
	Core.Primitives.FIFO<32, 512> FIFO1(...);
}

using Core;
entity Test
{
	Primitives.FIFO<32, 512> FIFO1(...);
}

using Core.Primitives;
entity Test
{
	FIFO<32, 512> FIFO1(...);
}

using Core.Primitives;
entity Test
{
	Core.Primitives.FIFO<32, 512> FIFO1(...);
}

Note that the using statement can be specified anywhere inside the root scope of the file (e.g. placing a using statement inside an entity declaration would result in an error message). However, it is recommended to place using statements in the beginning of the file to improve readability.