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Hotspot is a term that is used for a wireless service that helps share an internet connection on a device with multiple devices. Take a look at these pages:
http://www.webopedia.com/TERM/H/hotspot.html
http://compnetworking.about.com/cs/wireless/g/bldef_hotspot.htm
Hotspot is things like cafes which have wifi available at a price or free if you buy for example a coffee etc
Having taken a look at your recent posts on this forum, may be I can refer you to a few pages that will be really informative.
http://userguide.sonymobile.com/referrer.php?region=global-en&product=xperia-s
http://www.sonymobile.com/global-en/support/phones/xperia-s/support-documents/