Why is DNA replication (copying) described as semi-conservative?

DNA replication is said to be semi-conservative because of this process of replication, where the resulting double helix is composed of both an old strand and a new strand.

DNA replication is said to be semi-conservative because of this process of replication, where the resulting double helix is composed of both an old strand and a new strand ... Semiconservative replication would produce two copies that each contained one of the original strands and one new strand.