Samsung SGH-X427ZSACIN - Manual (Page 211)

Glossary
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card. It may be a four to eight-digit number and can be
changed, as required.
Proxy Server
A server that resides between a web client, such as a web
browser, and a real Web server and acts as an intermediary
between them. When some people browse a web site, their
browser is not actually connecting to the web server. The
request from their browser goes to a proxy server, and the
proxy server makes the request to the web server.
A proxy server can improve performance for groups of
users because it cache the results of all requests for a
certain amount of time. If a user requests a web page that
it already fetched for another user, it returns the page
instead of forwarding the request to the Web server, which
can be a time-consuming operation.
PUK (PIN Unblocking Key)
Security code that protects the phone/SIM against unauthorized
use. The PIN is supplied by the service provider with the SIM
card. It may be a four to eight-digit number and can be
changed, as required.
Roaming
Use of your phone when you are outside your home area (when
traveling for example).