Jidai is a Japanese word that means age and it is used to describe the condition of a bonsai tree that has been cultivated for a long time. The age of a bonsai tree can be seen in its thickness, bark, shape and color. A bonsai tree with good jidai shows an old and refined appearance that reflects the years of care and skill that went into growing it. Jidai is also related to other concepts such as koshoku (antique look) and sabi (elegant simplicity) that are used to appreciate the beauty of nature in water, stone and other elements. Jidai is one of the aspects that makes bonsai an art form and a way of expressing the harmony between humans and nature.