back and forth

"Back and forth" is a common phrase which describes something that goes in two directions. You can use "back and forth" to talk about traveling:

They have an apartment in London and a house in Boston, and just travel back and forth between them every few weeks.

You can also talk about something that swings or sways:

I'm just sitting here, watching the bamboo sway back and forth in the breeze.

This phrase appears in these lessons: