Guilloché (Guilloche), is an engraving technique in which a very precise intricate repetitive pattern or design is mechanically etched into an underlying material with fine detail.

it involves a technique of engine turning, called guilloché in French after the French engineer “Guillot”, who invented a machine “that could scratch fine patterns and designs on metallic surfaces”. The machine improved upon the more time-consuming practice of making similar designs by hand, allowing for greater delicacy, precision, and closeness of the line, as well as greater speed.
(From Wikipedia)