Greenfield and Brownfield investments are ways in which a company can expand into other countries. They are 2 different types of foreign direct investment.
Greenfield investment is when the company builds necessary resources from scratch in the new country. This could include building new plants, distribution centres etc. Greenfield option makes more sense if the business operations are unique and custom made for the company. It is more risky as it is the more expensive option of the two. If the operations are near one-of-a-kind, it would be cheaper to build it from scratch and operate it like existing parts of the business. A good example of this is the Gigafactory tesla is building in Germany.
Brownfield investment is when the company relies on acquiring existing companies and facilities. This makes sense when business operations are rather existing. In some cases, facilities are leased instead of purchasing. This could be an interim solution before companies can take the leap to build their own facilities in a new market.
This way of thinking can be applied to personal projects as well. Would it be easier to update your personal website by making tweaks or to rewrite it from scratch.