Is the GMT time zone is same all over world?

Is the GMT time zone is same all over world?

My server is running PHP. I am using gmtdate() function to inserting
records into my database from server. I just wonder whether time zone is
centralized by using gmatdate() function ?
Example:
One user creates entry from India and record is inserted into database
and
Second user create entry from USA/canada/france and record is inserted
into database.
Is that time will be same as I used gmtdate() function while inserting
record at server?