Red "slice" lines?

[DigitalChickster]

Hi all! I'm getting these weird red lines on my projects... they almost look like slices. I can't figure out how they got there... or how to get rid of them! Any ideas? Thanks! 
Update: I just figured out I can select them and delete them. But I'd still like to know what they are and how I must have accidently hit something that made them appear...

 

[Monika Gause · Accepted solution]

You can delete them via Object > Slice

You probably clicked something with the slice tool that you probably mistook for the knife tool.