I like to know what is hacking is in computer?
Please help me...

If you are looking for a definition, then it's basically what you see below that is from the following site. define:Hacking - Google Search (http://www.google.com/search?hl=en&safe=off&defl=en&q=define:Hacking&sa=X&oi=glossary_definition&ct=title)

Definitions of Hacking on the Web:

Unauthorized use, or attempts to circumvent or bypass the security mechanisms of an information system or network.
www.tsl.state.tx.us/ld/pubs/compsecurity/glossary.html (http://www.google.com/url?sa=X&start=0&oi=define&q=http://www.tsl.state.tx.us/ld/pubs/compsecurity/glossary.html&usg=AFQjCNH2HtGq3MAcVCGZLEc9hICaIpOkfg)
Accessing illegally or without authorization computers, accounts, equipment or networks belonging to another party, or attempting to penetrate security measures of another system.
www.searcycafe.com/wifiaup.php (http://www.google.com/url?sa=X&start=1&oi=define&q=http://www.searcycafe.com/wifiaup.php&usg=AFQjCNFugaZbEZqSSi-aq91iHw_Xj6uelQ)
Hacking means illegally accessing other people's computer systems for destroying, disrupting or carrying out illegal activities on the network or computer systems.
www.infosec.gov.hk/english/general/glossary_gj.htm (http://www.infosec.gov.hk/english/general/glossary_gj.htm)
The US Dept. of Justice defines Hacking as “All illegal access to a computer or a network”.
www.root777.com/computer-security/important-computer-security-terms-and-terminology/ (http://www.google.com/url?sa=X&start=3&oi=define&q=http://www.root777.com/computer-security/important-computer-security-terms-and-terminology/&usg=AFQjCNEAj6vGzibxqqqZRBlMDBESmJRfiw)
Hacking originally referred to programming. A quick and/or clever creation of a program or solving of a problem was referred to as “a hack”. A particularly adept programmer might be said to be a “good hacker”.
www.earthlinksecurity.com/security/articles/glossary/ (http://www.google.com/url?sa=X&start=4&oi=define&q=http://www.earthlinksecurity.com/security/articles/glossary/&usg=AFQjCNGOv5Ey2CA01jLQTn0O0cDPmhjOPg)