A sidepiece who is ok with and
even happy to be your sidepiece
even when you break up with your main piece. A portable sidepiece has no aspirations to be your primary relationship and will remain with you through multiple primary relationships.
Person A: I broke up with my
boyfriend.
Person B: So your side piece is gonna be your
main now?
Person A: No, he is a portable sidepiece, I can take him with me to the
next relationship.