In assembly language, an addressing mode is used to specify how to get the data for the instruction. Different instructions will make use of different addressing modes. The Motorola 68HC11 has 7 different addressing modes:

Inherent - The instruction requires no further data, as in ABA.
Immediate - The data for the instruction is found in memory immediately following the instruction itself.
Direct - The data is found within the first page of memory (the first 256 bytes), at the memory location specified, for example: ANDA $F6
Relative - The data is found a specified number of bytes ahead of, or behind the next instruction
Extended - The data is found at the memory location specified by the 2 bytes following the instruction, similar to direct, but allows you to access any memory location, not just the first page.
Indexed, X - The data is found at the memory location specified in index register "X".
Indexed, Y - The data is found at the memory location specified in index register "Y".