How does common app check for plagarism?

I know people have said that common app uses turnitin, but what does that mean? Do they scan similarities in content on the internet and also essays that have been previously submitted by students to common app? And are all colleges automatically checking for plagarism? I know some schools have “honor codes”.

There haven’t been any recent threads about this and I think this is important for applicants to know when applying and what they shouldn’t do because there can be serious consequences!