The difference between the two is in the application. A development length is the amount of rebar length that is needed to be embedded or projected into concrete to create a desired bond strength between the two materials. The lap splice length is the length two rebar pieces must overlap and be tied together to create a bond as if there was no break and the run is “continuous”. So simply put, development is rebar to concrete, splice is rebar to rebar. The lengths of both splice and development do vary. They are dependent upon different factors. These include but are not limited to concrete strength, rebar size, rebar coating and concrete cover or clearance. So when you see a chart on one project, it can differ from another for these reasons.
Development length is the length overlap of bars tied to extend the reinforcement length. is about 50 times the dia of bar is consider to safe.