In the PostgreSQL interactive terminal (psql), meta-commands are used for tasks that are not standard SQL, such as controlling the psql environment itself. The \connect command, which can be shortened to \c, is the specific meta-command used to close the current database connection and establish a new one to a different database. The command syntax is \connect dbname or \c dbname, where dbname is the name of the target database.

B. USE dbname; is the command for switching databases in other systems like MySQL and SQL Server, but it is not a valid command in PostgreSQL.

C. SWITCH dbname; is not a valid SQL or psql meta-command for any database-related operation in PostgreSQL.

D. SET DATABASE dbname; is not a valid command. The SET command is used to change run-time configuration parameters, not the database connection.

1. PostgreSQL 13 Official Documentation, psql Meta-Commands: The \connect or \c command is documented as the method to establish a new connection to a PostgreSQL server. The documentation states, "If the new connection is successfully made, the previous connection is closed."

Source: PostgreSQL 13 Documentation, Chapter 53. psql, Section 53.3. Meta-Commands.

2. PostgreSQL 13 Official Documentation, SQL Commands: The official list of SQL commands for PostgreSQL 13 does not include USE or SWITCH as commands for changing the database context.

Source: PostgreSQL 13 Documentation, Part VI. Reference, SQL Commands.

3. PostgreSQL 13 Official Documentation, SET Command: The documentation for the SET command confirms its purpose is to change session-level run-time parameters, such as SET searchpath TO myschema;, not to switch the database connection.

Source: PostgreSQL 13 Documentation, SQL Commands, SET.