Toxic Shock Syndrome- when a female leaves her tampon in too long. Doesn't happen every time you leave it in too long, but it's still not good. Tampon's should usually only be left in for 6-8 hours. Over night is also not the best thing. TSS is a harmful disease, and can cause death but not often.
"Sarah has TSS because she left her tampon in too long. Idiot."