The phrase "single strand" means that something is made up of just one piece or part, rather than multiple pieces that are connected or intertwined. Full definition
This technique involves folding a long single strand of DNA into a predetermined shape with the help of short «staple» strands. (frogheart.ca)
The flu virus stores its genetic information on single strands of RNA, which is very susceptible to degradation. (sciencemag.org)
Wear with anything from a bright coloured cocktail dress to a simple white tee — a long single strand of pearls is always effortlessly chic. (uptowntwirl.com)