What to learn from metastable level lifetimes in highly charged ions

There are various excited levels in highly charged ions that last for much longer than the typical "normal" levels, and for which the designation "metastable" has come into use. The causes for such metastability are explained in a tutorial manner and at a matching level of detail, sketching the underlying atomic physics as well as intricacies of the observations and attempted lifetime measurements. Some of these atomic systems are susceptible to external fields. Moreover, there are applications in highprecision physics experiments that rely on the particular longevity of the excited levels involved.