1.nounThe movement (of someone or something) forward followed by a return to the same position. May refer to a concept such as an emotional state or a relationship as well as a physical thing.
2.nounNegotiations or discussions between two or more parties, a dialog.
3.adjectiveGoing from one place or position to another and back again.
"The back and forth movement of the tide causes erosion of the coastline."