So, I just did a simple search, and lo and behold, Pew Research (The Donald's source of oversampling evil) had this to say:
Oversampling is the practice of selecting respondents so that some groups make up a larger share of the survey sample than they do in the population. Oversampling small groups can be difficult and costly, but it allows polls to shed light on groups that would otherwise be too small to report on.
Even the non-brained dead rightist organs (or some anyway) know the truth.
The conservative blogosphere is lighting up again with accusations of polling bias against Republican presidential candidate Donald Trump in his race against Democratic opponent Hillary Clinton. However, Trump supporters should avoid giving into this temptation to assume unfavorable results must be biased results. Clinton really is leading Trump, and by nearly 6 percentage points.