Vociferously means saying what you think in a loud, strong, forceful way. It is an adverb, so it tells you HOW someone speaks, complains, argues, or objects. The picture behind it is a room full of noise: people not just disagreeing, but disagreeing at volume, again and again, so that nobody can pretend they did not hear. It carries the idea of persistence as much as loudness — someone who complains vociferously keeps complaining until people pay attention. It is a formal, written word. You will find it in newspapers, in reports, in news on TV — "local residents vociferously opposed the plan" — but people almost never use it when they are just chatting with friends. In everyday talk we would say "they complained really loudly" or "they made a big fuss about it". A thing to notice: it is not really a compliment or an insult by itself. It can sound brave (standing up loudly for something right) or annoying (a customer shouting in a shop). The context decides. But it usually appears with words about disagreement — object, protest, complain, deny, oppose, argue — much more often than with words about agreement. You can say someone vociferously supported a plan, and it is correct, but that is the rarer half of how the word lives.

大聲疾呼地、激烈地（表達意見）；強烈抗議地