A niche is a very specific area that you can optimize for. For example, in a marketing book, I read about a struggling company that does translations of many different languages and was advised to develop a Niche of translating one language only. Despite their fear of leaving out a large potential audience, they followed the advice of the consultant and their business grew. Then after a time, they started to get asked if they translated other languages and they said that they did. After they were large enough they were not viewed as a jack of all trades of languages but instead showed a prime example of how powerful a niche can be.