Conjugated deoxyribonucleotides
To "conjugate" means to join or couple something together. Deoxyribonucleotides are the "letters" of DNA - A, T, C, and G. In biology/biochemistry, when you conjugate something you chemically modify it by adding something to it. Given the context of your question, the conjugated deoxyribonucleotides are fluorescently-labeled &mdash; a fluorescent dye has been covalently attached to it.