Zero page refers to the first 256 bytes of the memory map where an object can be addressed or referenced by a single byte. Some processors offer special instructions and/or addressing modes to take advantage of 8 bit accesses. The compiler uses two sections for zero page data. The .bsct section is used for initialized zero page data and .ubsct is used for uninitialized zero page data.
Using the zero page feature allows the compiler to optimize code to use direct addressing modes saving both code space and execution time. On some processors such as the HC05 and HC08 the compiler may also be able to use single byte pointers and data references.