Intellectual property is property which is owned by a person that is not tangible. It includes patents, trademarks, and copyrights. A person or company will still own the item, but it cannot be seen or held. It is usual that IP is leased or licensed to users for a set period of time and set fee with prohibitive restrictions against the user copying or sharing the material outside of that which is outlined within the specific contract.
Computer software and related technologies are the most popular IPs, but anything that is coined and registered as a person as unique and specific to them would be considered IP. Microsoft is a good example as when a person buys a computer with Windows running on it they are prohibited from copying the software to any other device other than the one that was purchased with it on, and it also has to be paid for annually (renewal).