1Ordinary, plain, or unremarkable — often used in the pattern "just an ordinary...".
彼はただの学生で、有名人ではない。
He's just an ordinary student, not a celebrity.
これはただの風邪だから、あまり心配しないで。
This is just an ordinary cold, so don't worry too much.
似ているだけで、ただの偶然だと思う。
They just look alike; I think it's merely a coincidence.
2Free of charge, gratis — commonly written in katakana as "タダ" in casual speech.
このコーヒーはタダですよ、遠慮なくどうぞ。
This coffee is free — please help yourself.
子供は入場料がただだ。
Children get in for free.
駅前でティッシュをただで配っていた。
They were handing out free tissues in front of the station.
3Unaffected, unharmed, or unpunished — usually appears in negative constructions like "won't get off so easily."
衝突事故だったが、幸いにも二人ともただで済んだ。
It was a collision, but fortunately both people came away unharmed.
今回は警告で済んだが、次はただでは済まないだろう。
This time it was just a warning, but next time it probably won't be so simple.
4Only, merely, just, simply — an adverb meaning that nothing more is involved.
私はただ黙って話を聞いていただけだ。
I was simply listening quietly.
彼はただ疲れているだけで、怒っているわけではない。
He's just tired; he's not angry.
ただ勉強しているだけでは、試験には合格できない。
Just studying alone won't get you through the exam.
それはただの噂に過ぎない。
That's merely a rumor.
5But, however, nevertheless — a somewhat formal conjunction used to add a qualification to what was just said.
旅行には行きたい。ただ、今は時間がないんだ。
I want to go on the trip. However, I don't have the time right now.
彼の意見は面白い。ただ、実現するのは難しいと思う。
His idea is interesting. However, I think it would be hard to put into practice.
今日は天気がいい。ただ、風がかなり強い。
The weather is nice today. However, the wind is quite strong.