Dictionary Definitions:
en·dur·ance/enˈd

o͝orəns/
Noun:
- The fact or power of enduring an unpleasant or difficult process or situation without giving way.
- The capacity of something to last or to withstand wear and tear.
stam·i·na/ˈstamənə/
Noun:
The ability to sustain prolonged physical or mental effort.
Both relate to the same general principle of having a level of physical fitness (combining aerobic and anaerobic facets) that will allow you to sustain moderate physical activity for an extended period.
Cardio training is training to increase the length of time you can perform moderate physical activity (within your aerobic threshold). A good way to measure what moderate is is by using conversation. If you can talk to yourself (actual talking) or to your training partner without deep breaths, you're not in a "moderate" zone. If you can talk, but need to stop to take a decent breath after every 5 or 6 words, you're working hard enough to increase your stamina/endurance.
In a survivalist sense, this is you jogging towards an area where you know there is game to hunt, or fish to catch, or trekking with a full pack up a mountain.
When you reach the point during intense exercise where you cannot talk, you have pushed yourself to the limit of your anaerobic threshold, which is where the body is using fast twitch muscle fibres and all available energy stored within your muscles.
Again, in a survivalist sense, this is you using the "flight" portion of "fight or flight", and you're running for your life - perhaps from a mountain lion, or a group of gun toting crazies.
Having participated in cycling, distance running and triathlon events for the last 17 years, I suggest running as a good way of increasing your endurance. Start with running a mile within 8 minutes, three times a week. If you can do that easily, increase your distance a half mile a week, or a mile a week if you feel comfortable. If you can run 5 miles within 30 minutes, you're doing better than the majority of the population, and could easily outrun them when they're chasing you and your food.
If you are going to do any sort of cardio training, get some good shoes and drink plenty of water. This makes all the difference.