Twining two (or more) threads, strings or fibres together to gain strength. The fibres are twisted and spiral around each other. The quantity of twines per meter, tells us something about the strength and sturdiness of the string. The more a string is twined, the stronger and sturdier the string will be.
Twining is done with yarn, before it is used to -for instance- make fabrics. It also happens -naturally- with protein; 1 peptide chain twists to the left, 3 peptide chains together (the triple helix) are twined to the right. The three twined peptide chains together, form a strong protein molecule.