What is open source in crypto?

Could you elaborate on the concept of open source in the realm of cryptocurrency? I'm curious to understand how it applies to this emerging technology and the significance it holds within the community. How does open source facilitate innovation and collaboration in the crypto space? What are some of the key projects or tools that leverage open source principles and have been instrumental in shaping the landscape? Moreover, how do open source projects ensure security and transparency in the development of cryptocurrencies and related technologies?