An offset from UTC.

Wikipedia calls it "the standard clock time observed during the period of summer daylight-saving in those European countries which observe Central European Time (CET; UTC+01:00) during the other part of the year."

Note the word "zone" does not appear in the above.

Based on a quick skim, CEST is a "time" not a "time zone".

https://en.wikipedia.org/wiki/Central_European_Summer_Time

https://en.wikipedia.org/wiki/Time_zone

https://en.wikipedia.org/wiki/Standard_time