星期六 means 'Saturday,' literally 'week six,' as it is the sixth day of the week in the Chinese system. It is one of the standard weekday terms and is commonly associated with the start of the weekend.
我们星期六去爬山怎么样?
Wǒmen xīngqīliù qù pá shān zěnmeyàng?
How about we go hiking on Saturday?
星期六不用上班,我想在家好好休息。
Xīngqīliù bùyòng shàngbān, wǒ xiǎng zài jiā hǎohǎo xiūxi.
There's no work on Saturday — I want to rest well at home.
他每个星期六都会去健身房锻炼。
Tā měi gè xīngqīliù dōu huì qù jiànshēnfáng duànliàn.
He goes to the gym to exercise every Saturday.