a) Served Needs: These are needs that customers know and are fulfilled by different businesses or the government. 

For example: the need of travelling from one place to the other is taken care of by both, private bus services and government bus services. 

b) Partially-served Needs: These are needs which are served through different products or services, but the customer is not completely satisfied and still faces problems while using. 

For example: people always used taxis and auto rickshaws to go to different places, but they face problem in finding one on time, and paying a reasonable amount for it.

c) Unserved and Known Needs: These needs are known by the customers, but not fulfilled by anyone in the market. 

For example: people in small towns do not have electricity supply at all times, and therefore their children cannot study after sunset. A company realized this problem and created solar-lamps, which get charged during the day and can be used at night. 

d) Unknown Needs: These are needs that people have, but are not aware or do not expect for it to get solved by a business. 

For example: people 10 years ago did not know that it will be possible to make video-calls across cities or countries. But through innovation, entrepreneurs and innovators found the technology to make this happen.