The informal term FrankenMech refers to 'Mechs that combine parts of different 'Mech designs, usually to the point of not being based on any one particular parent design. They may either have been constructed entirely out of spare parts, or otherwise have been modified beyond recognition with parts from other units.
The somewhat more formal term HybridMech, which is often used synoymously, technically has a different meaning: It refers to 'Mechs built with wildly different technologies (typically combining Inner Sphere and Clan technology base). HybridMechs often are FrankenMechs, but exceptions are possible.
FrankenMechs became somewhat common during the Succession Wars as factories, spare parts, and reliable supply lines became increasingly rare. They are very rare and typically one-of-a-kind individual designs, although some (like the Wolfman) may in fact have been created more than once.
In the Succession Wars era some new 'Mech designs were designed by recombining components of other, older 'Mech designs. These are generally treated as new, distinct 'Mech designs although they are arguably just standardized FrankenMechs put into regular production. Notable examples include the Merlin and the Cataphract.
- Strategic Operations, p. 189, "FrankenMechs (Optional)"