LDT (and GDT) entries which point to identical memory areas are called "aliases". Aliases are also typically created in order to get write access to code segments: an executable selector cannot be used for writing. (Protected mode programs constructed in the so-called "tiny" memory model, where everything is located in the same memory segment, must use separate selectors for code and data/stack, making both selectors technically "aliases" as well.) In the case of the GDT, aliases are also created in order to get access to system segments like the TSSes.