From the ACI318 bar overlap and development length are divided into 2 cases, top bars and other bars. The definition of other bars applies to any vertical bar, horizontal bar with concrete thickness less than 300 mm below. Top bar is any horizontal bar with concrete thickness exceeding 300 mm below the bars. In some cases, detailers consider the bottom bar development length terminated inside a pile cap or any other section with thickness exceeding 300 mm from below as other bar which is not right! Let me know if you need further details.