There are many reasons why a person may have periods of time during his/her career when they have not been working.  Explaining these gaps can be complicated, and a deterrent to the recruiter, if not handled properly.  If the time of unemployment is only a few months, you can eliminate specifying months on the resume which may camouflage the time out of work.  If you were unemployed for a longer period, as a parent, for medical issues, for education, to research a new career, or being laid-off,  a short line of explanation is all that may be needed.  Some examples might include: 

• Stayed home to care for elderly parent                      2021-2023
• Moved to a new location for spouse’s job                   2020-2021
• Medical issues requiring lengthy recovery                 2021-2022

Nothing more needs to be stated or explained on the resume.  Further elaborations can be addressed either in the Cover Letter or in the interview.  If you have been unemployed without a great reason, it might be preferable to reorganize the resume to focus on strengths and skills, and less on chronology, so that the hiring manager will evaluate your ability against the position description, and less on the gaps in your work history.