* Double helix: This refers to the shape of the DNA molecule, which resembles a twisted ladder. The two strands of DNA are wound around each other, forming a helix.

* Watson-Crick model: This refers to the specific model of DNA structure proposed by James Watson and Francis Crick in 1953. This model describes the double helix structure and the base pairing rules (adenine with thymine, guanine with cytosine).