It is an adverb that means “to go out of one’s way“. It is used to describe situations in which someone tries very hard to do something for themselves/someone else.
When you describe others' actions using this word, it usually indicates your gratitude to others. On the other hand, when you describe your actions using this word, it is usually used in a sarcastic way. It indicates that you don’t want to do something but you do.
After Amy finished for the day, she noticed that Meg left her wallet at the office. And then Amy is calling Meg.
- Amy: I found your wallet on your desk. Do you want me to bring it to your place?
机の上に、(メグの)財布があったよ。持って行こうか？ - Meg: Oh, thank you. But I think that you’ll have to make a detour on the way back to home if you come here. Is it okay?
あっ、ありがとう。でも、家に来たら、遠回りになるよね？いいの？ - Amy: Sure. It isn’t a big deal. I’m already on my way.
うん。大した事ないよ。もう向かっているよ。 - Meg: Thank you for going out of your way for me!
わざわざ、ありがとう！
Ken is busy with the current projects and he doesn’t have time to take care of the new project.
- Leo: I sent you several emails about the new project. Have you read them already?
新しいプロジェクトに関するメールを送った。もう見た(or読んだ)？ - Ken: No, I’m sorry. But I’ll check them sometime in the afternoon.
ううん。午後には見るよ。 - Leo: You don’t need to bother reading them now. You can go through them after your current tasks settle down.
今わざわざ確認する必要はないよ。今のプロジェクトが落ち着いたら、目を通してよ。
Ken is going on a business trip to Osaka tomorrow.
- Leo: What are you doing in Osaka?
大阪で、どんな仕事をするの？ - Ken: I’m just meeting the new branch manager. It’s tiring going all the way there just for that.
新しい支社長に挨拶するだけ。それだけの為に、わざわざ行くのは面倒くさいよ。