The noun 带子 (dàizi) means "strap," "belt," "ribbon," or "band." It refers to a long, narrow strip of material used for fastening or tying. For example, 解开带子 means "to unfasten the strap."
这个包的带子断了,你能帮我修一下吗?
Zhège bāo de dàizi duàn le, nǐ néng bāng wǒ xiū yíxià ma?
The strap on this bag broke. Can you help me fix it?
她用一根红色的带子把头发扎了起来。
Tā yòng yì gēn hóngsè de dàizi bǎ tóufà zā le qǐlái.
She tied her hair up with a red ribbon.
鞋子的带子太长了,走路容易绊倒。
Xiézi de dàizi tài cháng le, zǒulù róngyì bàndǎo.
The laces on the shoes are too long, making it easy to trip while walking.