Lemniscate is not a term most of us use but we have seen the figure the term represents.
A lemniscate is a figure-eight shaped curve. Many, like me, refer to it as the infinity symbol.
The label lemniscate makes sence because it comes from the Latin word lemniscatus—meaning decorated with ribbons. This in turn relates to the Greek Island of Lemnos. On this island, ribbons were worn as decorations. Some think the word derives from the wool that the ribbons were made of.
The first usage of the word leminscate was in about 1781.
New Latin lemniscata, from feminine of Latin lemniscatus with hanging ribbons, from lemniscus