An approach to organisation or planning that is built up from basic details rather than from a guiding principal or theory. It is a form of organisation often associated with the democratic involvement of many individuals rather than one governed by an individual or small group.
Bottom-up is inextricably linked with its converse - top-down. Both are from the mid-20th century and it's appropriate that the first citation of bottom-up also includes top-down: That's from the 1942 edition of Harvard University's Quarterly Journal of Economics:
"In the long run it is part of the larger question of whether 'bottom-up' control can be as efficient as 'top-down' control."
That debate is still active in many fields, economic development included. On the one hand there's the bottom-up adherents of small-scale democratically managed development championed in E F Schumacher's Small is Beautiful. On the other there's the top-down approach taken by large corporations.