The word להשליך means to throw, to cast off. It’s a הפעיל verb of the root ש.ל.כ , probably related to the root ש.ל.ח meaning sending.
This word appears mainly in Biblical or poetic Hebrew, as in:
And they shall throw them (stones) away outside of the city, to an impure place. (Leviticus 14:40)
For example, you may have seen this inside an Israeli bus:
Throwing garbage out of this vehicle is forbidden.
השלכה also means consequence – a spinoff, if you will, of an action.
You know that what you’re about to do will have consequences.
השלכה also refers to the psychoanalytic concept of projection – casting one’s unknown or unwanted self concept onto another person.