Production - standardized knife platform produce en mass and put together on an assembly line.
Midtech - I would think would be above production in that they have more exacting specifications and maybe a non standard blade alloy. I would also assume that they would be better fit and finish that a production knife as they are not produced at assembly line speeds.
Custom - Everything on the knife is made and fitted by hand. Usually a one off unit or very limited run of units. Fit and finish on a good custom knife exceeds at care and craft. Can include such things as mosaic pins, specialized handle materials such as fossil ivory or exotic wood, select material usage in liners and possible non standard locking blade designs on folding knives. Unusual blade and handle dseigns as well as unusual blade fabrication techniques such as pattern welded steels.