Life span, the period of time between the birth and death of an organism.
It means the drawing, painting, sculpture, etc.. has the same pattern or looks equal on both sides.
As the Vietnam War raged in 1969, John Lennon and his wife Yoko Ono held two week-long Bed-Ins for Peace, one at the Hilton Hotel in Amsterdam and one at the Queen Elizabeth Hotel in Montreal, each of which were intended to be nonviolent protests against wars, and experimental tests of new ways to promote peace. The idea is derived from a "sit-in", in which a group of protesters remains seated in front of or within an establishment until they are evicted, arrested, or their demands are met.