I noticed this when I was listening to Momoiro Clover Z's 「行くぜっ！怪盗少女」, which had this line: 「土日｛どにち｝はよろしくね 週末ヒロインです」. I understand that 土日 means 土曜日 + 日曜日 = weekend, i.e. 週末. Thus, can 土日 and 週末 be used interchangeably, or are there different nuances in 土日 and 週末?
There is also the term 休日, which I understand as referring to "days off", i.e. weekends plus public holidays 祝日. However, can 休日 be used interchangeably with 週末/土日 as well? (Because I think I might have seen this usage in Japan, but I may be wrong.)