什么是low-level code

大新

To facilitate the MRP processing ,each item in the BOM is given a low-level code (LLCthis code indicates the lowest level in a bill of material that a particular part is
ever used.end items(that are not a part of any other item) have LLCs of zero.

在这段文字中不理解LLC的具体意思，请达人帮忙解释一下。