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: 
You are dealing with **[terminology](https://en.wikipedia.org/wiki/Terminology)** (a discipline of applied linguistics) and **[term extraction](https://en.wikipedia.org/wiki/Terminology_extraction)**. You are looking for **terms**. The quoted wikipedia articles will give you some starters for further reading.
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.