There are both variants in the wiki:
https://wiki.postgresql.org/wiki/Don't_Do_This#Don't_use_tim...
> Don't use the timestamp type to store timestamps, use timestamptz (also known as timestamp with time zone) instead.
> Why not?
> timestamptz records a single moment in time. Despite what the name says it doesn't store a timestamp, just a point in time described as the number of microseconds since January 1st, 2000 in UTC. You can insert values in any timezone and it'll store the point in time that value describes. By default it will display times in your current timezone, but you can use at time zone to display it in other time zones.
> Because it stores a point in time it will do the right thing with arithmetic involving timestamps entered in different timezones - including between timestamps from the same location on different sides of a daylight savings time change.
> timestamp (also known as timestamp without time zone) doesn't do any of that, it just stores a date and time you give it. You can think of it being a picture of a calendar and a clock rather than a point in time. Without additional information - the timezone - you don't know what time it records. Because of that, arithmetic between timestamps from different locations or between timestamps from summer and winter may give the wrong answer.
> So if what you want to store is a point in time, rather than a picture of a clock, use timestamptz.