It's basically the concept of using "different bacteria inhibiting or bacteria killing factors to achieve a safe product with an optimal shelf life". In other words, it's about combining different preservatives at lower levels to achieve good preservation of products. A huge part of this process is taking into account the physiology and behaviour of the microflora (aka beasties) that might contaminate our products, looking at things like homeostasis, metabolic exhaustion, stress reactions, and how they react to temperature, pH, ingredients in our products, and so on.
The hurdles in this process are retarding growth, removing organisms, and creating safe products. Our goal is to overcome each of the hurdles to create an awesome product that won't be enticing to bacteria, yeast, and moulds.
We can use this concept at home without having to take an advanced course in biology in a few different ways. The first is to use distilled water and follow good manufacturing processes like heating and holding. The second is to consider the packaging we use - choosing disc caps or flip tops over screw tops, for instance - and consider making products single use or making smaller batches. And the third is to consider the ingredients we use.
Although I love my botanicals ingredients like aloe vera, hydrosols, extracts, and proteins, they are notoriously hard to preserve and will attract the beasties. If you want to use these ingredients, ensure you are preserving them well with a suitable preservative at the maximum safe level.
So now you know a little more about hurdle technology. So why the picture of Hermes limboing under the stove to illustrate the point? I like Futurama.