What is implantation bleeding

So at 8 DPO when i went to the bathroom there was a stop of pinkish blood on my TP. but I haven’t seen it since also the next day and every day since (I am now 11 DOO) I have felt like there’s a ball sitting on my uterus. Was that implantation bleeding? I should add I have PCOS this is my first month really TTC. AF isn’t due till Saturday.

Added on: today I ate a breakfast I always eat spice sausage with a little syrup and it did not say down. I threw it right back up.