Explain between Incident, Incident Request and Service Catalog

Explain between Incident, Incident Request and Service Catalog

Refer the attached file, I would like to know that what's different Incident, Incident request and Service Catalog on SDP system?  I knows the service catalog is kind the request new service such as install software etc. but I am not sure about the Incident and Incident request. Please assist me to clearly this. 



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