Question: 1. Go to this website: <http://parts-of-speech.info/>
2. Now go to this Wikipedia article: <https://en.wikipedia.org/wiki/Evolutionary_psychology>
3. Grab the first paragraph and feed it into POS tagger to see the
tags. This is an image of the result:

[![parts of speech tagging result](https://i.stack.imgur.com/9cgNz.png)](https://i.stack.imgur.com/9cgNz.png)

However, as human beings, to understand this text, we need to understand some concepts that are denoted by more than one word:

* Evolutionary psychology
* Natural science
* Natural selection
* ...

These are technical terms that mean more than simply a bunch of words and they are not tagged. For example, if you know **natural** and **selection**, you don't necessarily know **natural selection**.

Is there a technical term to refer to concepts which are composed of more than one word? Also, is there a way to identify them in a given text? In other words, what is the name for technical terms in Linguistics, and how does find technical terms using NLP algorithms and techniques?

Answer: 
These are called multi-word expressions (MWEs). Before we put things into a POS tagger, we need to perform another process known as *tokenisation* to separate characters into words. This is especially important in Chinese, where there are no whitespaces at all, but is also needed in English, where strings surrounded by word boundaries (in the sense of regex) are not always words either.

For solutions, you can [search on Google scholar](https://scholar.google.com.hk/scholar?q=multiword%20expressions&btnG=&hl=zh-TW&as_sdt=0%2C5); there is a huge literature on that. :)
You may also want to look into **Idioms**. An Idiom is a phrase (series of words, usually) whose meaning is not composed of its parts, at least not without a layer of metaphorical or (usually lost) historical meaning. For example,

* The fly [kicked the bucket] (to mean the fly died)

is an idiom since knowing what [kick] and [the bucket] mean does not allow one to derive what [kick the bucket] means. It may be productive to look into whether or not [natural science] can be derived from what [natural] and [science] means in the technical sense.