A concept pioneered by semanticist Anna Wierzbicka. The idea is, keeping in mind that the customs of your tribe are not laws of nature, the only way to create definitions of things that are not biased by culture is to use a natural semantic metalanguage consisting of words that are found, with the same fundamental meaning, in every language in the world, and are themselves indefinable--that is, you can't say what they mean without complicating things.
Here are the primitives I know of now; this is probably neither final nor complete (if I had more of her books here to read I could probably say better). I won't bother explaining most of them because you probably already know what they mean (that is, of course, the whole idea).
Amounts and determinatives
Stuff going on:
Note that the grammatical categories these words fall into in English are not necessarily going to be the same in other languages; e.g., another language may use a noun to express what we use the verb "to feel" for.
Here's a homemade explication of an abstract concept, using this NSM approach. (If I've botched it horribly, don't laugh.) ;p
X felt something
because X thought something
Sometimes a person thinks something like this:
I want to do something
Someone is here
Because of this, I can't think: I will do what I want
I want this person to not be here
Because of this, this person feels something bad
X felt something like this
because X thought something like this
...that's about as close as I can get to explaining frath.
For more information, read apparently just about any book by Anna Wierzbicka. It will make the top of your head come off.