We use the conjunction whereas to indicate a contrast between two facts or ideas:
He loves foreign holidays, whereas his wife prefers to stay at home.
Whereas most new PCs have several USB slots, older ones often only had one.
Whereas means the same as while in sentences expressing contrasts. It does not mean the same as while when while refers to time:
The south has a hot, dry climate, whereas/while the north has a milder, wetter climate.
The secretary took care of my appointments while I was away from the office.
Not: … whereas I was away from the office.
