Population vs. Sample Can you use population to refer to a particular population? For example the population of women in Maths Class, from which we can take a sample to measure the height in order to make a judgement of the height of all the women in that class (i.e., the population). 
This question is different from previous Population vs. sample questions, by addressing to the meaning and how the term "population" can be used. As I mentioned in the question: is it correct to say "population of women in Maths Class"? Or once you add some extra context to the term "population" it is no longer a population, but a sample, or something else.
 A: The word "population" does not refer to all living people in the world. That is the generic understanding of the word, and not the statistical understanding.
Statistically, population refers to the class/group of units (or individuals in this case) about whom you want to make some inference. If the group you want to make the inference on is "women in Math 101 in Spring 2016 at UCLA" then that is your population. You can now go ahead and gather a sample or do a census study on that population.
A: You correctly distinguish in the title population from sample. Unless you gather a complete sample (eg census), then your population can only be inferred through, indeed, statistical inference from a sample.
The whole process of statistical inference rests on explicitly providing you instruments to navigate this mental voyage from your sample at hands to the population you'll never (likely) be able to appraise in full.
For instance, confidence/credible intervals tell you how much the inferential estimates you have gathered from your sample can be considered with confidence or credible.
You can find other very good takes at this issue in CrossValidated, as well as elsewhere:
What is the difference between a population and a sample?
https://en.wikipedia.org/wiki/Sampling_%28statistics%29
http://www.dissertation-statistics.com/population-sample.html
http://www.sagepub.com/sites/default/files/upm-binaries/41398_40.PDF
