what is quoted_identifier in sql server code example

Example 1: QUOTED_IDENTIFIER

SET QUOTED_IDENTIFIER OFF
GO

-- Create statement fails.
CREATE TABLE "select" ("identity" INT IDENTITY NOT NULL, "order" INT NOT NULL);
GO

SET QUOTED_IDENTIFIER ON;
GO

-- Create statement succeeds.
CREATE TABLE "select" ("identity" INT IDENTITY NOT NULL, "order" INT NOT NULL);
GO

SELECT "identity","order"
FROM "select"
ORDER BY "order";
GO

DROP TABLE "SELECT";
GO

SET QUOTED_IDENTIFIER OFF;
GO

Example 2: QUOTED_IDENTIFIER

SET QUOTED_IDENTIFIER must be ON when you are creating or changing indexes on computed columns or indexed views. If SET QUOTED_IDENTIFIER is OFF, then CREATE, UPDATE, INSERT, and DELETE statements will fail on tables with indexes on computed columns, or tables with indexed views.