" Build " is where code is written, It is step 4 in SDLC(software Dev Life Cycle) 
a specific build task is based on a specific feature request

SDLC include 
1-3. planning, analysis, design, 
4. development (or build) , 
5-7. testing, implementation, and maintenance.

I Agile development, the build team receives user stories that tells 
the build team what user sees and what feature the user needs. Once the tester
makes sure the new feature matches what the user needs, the build task 
is closed.