What we usually mean by chronic stress is a low-level stressor or stressors, that are pervasive and inescapable but not obviously threatening, like a chronically stressed parent or parents when we are young or being in a highly polluted environment. It could also be an extremely demanding workplace, or a partner who is always unwell. A lot of shock traumas in a row could also be perceived that way though, such as being in a war zone, or having a series of accidents, but the effect will probably be slightly different, as chronic stressors usually lead to an embedded freeze response, while a series of shock traumas may not do that.