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' - 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."
The debate is still active in many fields, economic development included. On the one hand there are the bottom-up adherents of small-scale democratically managed development as championed by E F Schumacher in Small is Beautiful; on the other hand is the top-down approach taken by large corporations.