From RFC 1034 (Domain Names — Concepts and Facilities — Implementation and Specification — Application and Support)
http://www.ietf.org/rfc/rfc1034.txt?number=1034
When a user needs to type a domain name, the length of each label is
omitted and the labels are separated by dots ("."). Since a complete
domain name ends with the root label, this leads to a printed form which
ends in a dot. We use this property to distinguish between:
- a character string which represents a complete domain name
(often called "absolute"). For example, "poneria.ISI.EDU."
- a character string that represents the starting labels of a
domain name which is incomplete, and should be completed by
local software using knowledge of the local domain (often
called "relative"). For example, "poneria" used in the
ISI.EDU domain.
*** So each part of the full name is a label...
www. label
domainname. label
com label
www.domainname.com complete domain name
from RFC 1035: Domain Names
http://www.ietf.org/rfc/rfc1035.txt?number=1035
2.3.4. Size limits
Various objects and parameters in the DNS have size limits. They are
listed below. Some could be easily changed, others are more
fundamental.
labels 63 octets or less
names 255 octets or less
TTL positive values of a signed 32 bit number.
UDP messages 512 octets or less
** so a domainname as we consider it can be 63 characters long with the entire address string being limited to 255....
I use subdomains sometimes just for fun... Don't know if I still have it on my server, but at one point I had stuff like....
girls.who.like.to.fuck.and.suck.at.partyafterdark. com and that is what is limited to 255
Hope this helps