Virtual Tables

Directly from BOL:

DML trigger statements use two special tables: the deleted table and the inserted tables. SQL Server automatically creates and manages these tables. You can use these temporary, memory-resident tables to test the effects of certain data modifications and to set conditions for DML trigger actions. You cannot directly modify the data in the tables or perform data definition language (DDL) operations on the tables, such as CREATE INDEX.

They are described as virtual because they do not actually exist in the same manner as other tables do (e.g., they cannot be seen in the catalog views) and because they exist/are accessible in very specific contexts.

In addition, views can be thought of as virtual tables since a view can be used in the same manner as a table.