The Turnitin similarity/originality report checks each student's work against Turnitin's database of web pages, publications, and previously submitted assignments, producing a report showing:
where the student's writing matches Turnitin's database
the percentage of the student's writing that matches Turnitin's database.
It is natural for student submissions to match Turnitin's database as students will include quotes, references and common words or phrases in their assessments. As such the score in the report does not tell you if a student has breached academic integrity, and the report needs to be interpreted to determine if the matches are acceptable or not.
This entry relates to the 
The Turnitin similarity/originality report checks each student's work against Turnitin's database of web pages, publications, and previously submitted assignments, producing a report showing: