Meanwhile, whereas: trong khi đó

Trong khi đó opens a sentence that sets a second fact beside the first, for contrast: Giá xăng giảm. Trong khi đó, giá điện lại tăng. Petrol prices fell. Electricity prices, on the other hand, went up. English might say "meanwhile", "whereas" or "by contrast".

It usually starts a new sentence, or the second half after a comma or semicolon. The two halves often point in different directions: one figure rises and another falls, one city copes and another struggles. Lại (instead, contrary to what you'd expect) often appears in the second half to stress the surprise.

It can also be "meanwhile" in time: two things going on at once in different places. Trong khi đó, tại miền Trung, mưa lớn vẫn tiếp diễn. Meanwhile, in central Vietnam, heavy rain continued.

Compare trong khi without đó. Trong khi + a statement joins two halves inside one sentence (trong khi giá điện tăng, while electricity prices rose), and in speech it's simply "while". Trong khi đó stands at the front and points back to the whole previous sentence.

It's one of the most common connectors in news reports, on every news site, and frequent in papers. In conversation, the everyday equivalent is còn: Xăng giảm, còn điện thì tăng. Petrol's down, but electricity's up.