Synthetic programming (HP-41)
Synthetic programming (SP) is an advanced technique for programming the HP-41C and Elektronika B3-34 calculators, involving creating instructions (or combinations of instructions and operands) that cannot be obtained using the standard capabilities of the calculator. Some HP-41C instructions are coded in memory using multiple bytes.
Source: Wikipedia — Synthetic programming (HP-41) (CC BY-SA 4.0)