1Jeans — casual trousers made from durable denim fabric, commonly worn in everyday life.
今日、新しいジーンズを買って履いてみた。
I bought new jeans today and tried them on.
あの店のジーンズはサイズが豊富で履き心地がいい。
The jeans at that shop come in many sizes and are comfortable to wear.
ジーンズにTシャツというラフな格好で出かけた。
I went out in a casual outfit of jeans and a T-shirt.
この会社は面接でもジーンズで来ていいそうだ。
Apparently at this company you can even wear jeans to an interview.
2The 'denim fabric' sense, inherited from English 'jean'. In practice, modern Japanese almost always uses デニム to refer to the fabric itself — ジーンズ is essentially only used to mean the pants (see sense 1).