A conjunction meaning "but" or "however," used to show contrast (similar to しかし or だが), often slightly formal.
行きたいだけれども、予定があって行けない。
I want to go, but I can't because I have plans.
説明はわかりました。だけれども、もう少し詳しく聞きたいです。
I understood the explanation. However, I'd like to hear more details.
彼は親切だ。だけれども時々厳しいところがある。
He is kind. However, he can be strict at times.