1A casual spoken contraction of この間 ("the other day," "recently") — refers to something that happened not long ago; extremely common in everyday conversation.
こないだはありがとう。助かったよ。
Thanks for the other day — you really helped me out.
こないだ見た映画、すごく面白かったよ。
The movie I watched the other day was really interesting.
こないだ、駅前でばったり田中さんに会った。
I ran into Tanaka-san by chance near the station the other day.
こないだの件、どうなったか教えてくれる？
Could you let me know what happened with that thing from the other day?