empty nest

/EH1 M P T IY0 N EH0 S T/
noun
  1. 1

    A home or a family where the children have grown up and moved away.

    โ€œRather than sit around her empty nest reminiscing about bygone days, she converted her sons' bedroom into an office and launched an at-home business.โ€

Source: https://en.wiktionary.org/wiki/empty%20nest