Retirement is that happy point when you can stop working entirely. Or, if you drop the day job but keep a fun part time job you may refer to that situation as semi-retirement. In the US a variety of federal laws regulate retirement benefits, with varying benefits becoming available in varying amounts at differing retirement ages.
In general, US retirement age is 65 but many individuals, depending on year of birth and other factors, may chose to retire as early as 62 or as late as 67. Generally, retirement benefits increase as age at retirement increases.