I also think in just 3 "terms", with nothing shorter than short term or longer than long term. So for me surviving in the long term would mean surviving indefinitely. It would mean learning about crops, bee hives, rewiring power-generators, preserving knowledge for future generations etc. I find this stuff interesting, partly because I like science fiction, but it is not something I am actively preparing for. Although it includes the end of the world as we know it, it would also include the kind of skills that would let you survive in the wilderness for years. Much of it is Ray Mears-style bushcraft. The emphasis on sustainability.

Surviving in the short term would mean surviving the immediate danger. Getting out of the collapsed building, getting home, surviving the first night. The time period would usually be measured in hours, short enough that food is not an issue. Usually water and shelter would not be issues either, unless you are in the kind of hositile environment where dehydration or hypothermia are immediate threats.

The medium term is everything in between. The time frame is long enough that you need to worry about consumables - water, food, petrol, batteries etc - but your provision for these doesn't have to be sustainable. There should be some definite end to the crisis in sight, and the aim is to survive in relative comfort until then. You have enough time to think, take stock, plan and build.

So, for example, if the problem is shelter, a bin-liner could be a short-term solution, good to get you through one night. A small tent or built shelter would serve in the medium term. For the long term you want something that can take the worst of whatever the climate will throw at it, year in and year out.

Short term: a 500ml bottle of water. Medium term: water filter or large stockpile in the basement. Long term: a fresh water stream or well.

Short term: go hungry. Medium term: meals-ready-to-eat. Long term: fishing and hunting kits.

Short term: Photon keychain light. Medium term: Surefire's best with a stockpile of batteries. Long term: learn how to make candles.

Every-day Carry and Personal Survival Kits are mostly aimed at the short term, with some exceptions. Some kits include cordage for building shelters, which is more of a medium term concern. Fishing kits are long-term. Bug-out Bags are mostly aimed at medium-term survival. Deep bushcraft knowledge, such as how to build and use a fire-drill, is long-term. You can of course use long-term, sustainable solutions for medium-term and short-term problems.