The difference between a disaster, shtf, collapse, and TEOTWAWKI
Disasters happen often. They're localized events on a small or large scale and affect the populations of wildlife and humanity in that area. Some initial issues happen, loss of supply chains, security declines, supply chains and personnel are dispatched, most people get utilities back on, security increases, and most of the people slowly get back on track. Some deaths based upon exposure.
Some disasters are worse than others. The SHTF and long complex issues arise from other events like disease, malnutrition, stress, violence, pre-existing poverty, lack of preparedness, etc. Hurricane Katrina was in this category and continues to create issues for those people most affected and it may be a decade (if at all) for them to get back to normal. Since that area is prone to new disasters, it's reasonable to assume another hurricane might happen in the interim. Some deaths based upon exposure and violence and foolish reactions.
SHTF means the area could be wide-spread and persistent. If it does, then it might lead to anarchy and collapse of civilization in that affected area. In a collapse, it a systemic issue and this could result in severe disruption of supply chains and transport of security into ones and then they draw down upon existing supplies besides civilian needs. Some collapses lead to revolution. All will have deep political consequences. Those who prepare can help their communities to have higher security by teaching skills. There are many more deaths, particularly based upon weather. High amounts of violence. Many unnecessary deaths from medical issues. Starvation. Dehydration. Stalingrad fits here, as does many war-time events.
The end of the world as we know it (TEOTWAWKI) means that the collapse was so systemic that it went global. Massive amounts of anarchy and violence occur. It's so widespread that it's impossible to reestablish order. Looting occurs initially by unprepared folks to survive, but ultimate lacking skills they die. Survivors “liberate” by salvaging materials from stores for long term use to reestablish utilities, agriculture, sanitation, etc ...for if they don't then everyone will die. Civilization probably never comes back, only pockets of it.