A time zone is an offset from the time in Greenwich, England.
The time in Greenwich was once known as Greenwich Mean Time (GMT).
It is now known as Coordinated Universal Time.
You specify a time zone using either an offset from UTC or the name of the region.
When you specify an offset, you use HH:MI prefixed with a plus or minus sign:
+|-HH:MI
where
+ or - indicates an increase or decrease for the offset from UTC.
HH:MI indicates the time zone hour and minute for the offset.
You may also specify a time zone using the name of a region.
For example, PST indicates Pacific Standard Time, which is seven hours behind UTC.
EST indicates Eastern Standard Time, which is four hours behind UTC.
Quote from:
Oracle Database 10g SQL (Osborne ORACLE Press Series) (Paperback)
# Paperback: 608 pages
# Publisher: McGraw-Hill Osborne Media; 1st edition (February 20, 2004)
# Language: English
# ISBN-10: 0072229810
# ISBN-13: 978-0072229813