I would try to put it in simple words. So, I would say that bitcoin is an asset in a digital form that is impossible to copy. Also, it can be used as a mean of payment for goods and services online with transaction fees that sizably lesser than fees of any traditional electronic payment system. It's always easier to understand something using examples, so Id draw a parallel between bitcoin and gold. They both are assets, which people use to secure their money. They can be mined and have a limited amount that makes them valuable that excludes the possibility of inflation. In my opinion, it also important to mention the blockchain technology, which has proved its serviceableness, and has been massively adopted by large companies.