It is an adjective that means "to be awkward". It is used when describing situations in which you feel uncomfortable, embarrassed or find it difficult to deal with.
Meg and Amy went to the same party last night, but they didn't see each other.
- Meg: Were you really there yesterday?
昨日は本当にパーティーに来てた？
Amy: Yeah, but I also couldn't find you. There wasn't anyone I know and I had to talk to someone I don't know. It was awkward.
うん。でも、メグを見つけられなかった。知り合いがいなくて、初対面の人と話さなきゃいけなかったよ。気まずかった。
Meg: Same here. And I was the only one in a casual dress. That felt uncomfortable.
私も。それに、カジュアルな服を着ていたのは私だけだった。気まずかったよ。
Ken was assigned a new project and he is complaining about his team.
- Leo: How is the new project going?
新しいプロジェクトはどう？
Ken: I’m not really used to my team. I'm the only guy in 10 members. I feel like I don’t fit in.
まだチームに慣れてない。10人中、男は俺一人だけ。なんか、気まずくってさ。
Leo: Lucky you!
いいじゃん！
Ken: No way! There is my ex who I broke up with last month. Hmm, I feel like there has been an awkward tension between me and her.
よくないよ！先月別れた元カノ(=元彼女)もいるんだ。あー、何となく気まずいんだよね。
Leo: If I could switch with you, I'd love to join the team. Hahaha..
代わってあげられたら、いいのに。笑...