A Made to Measure custom suit is a step above an "Off The Rack" Suit but below a Bespoke Made Suit.
Made to Measure (MTM) custom suits involves a fitting for the purpose of producing a custom suit from a preexisting pattern. In this case, certain posture adjustments can be made for low shoulder, stance, prominent chest etc. These adjustments are made by manipulating a standard pattern and marking it with chalk before finalizing, hence no original pattern is created.
Across the board MTM programs vary depending on the clothier, most of these custom suit programs offer personalization options
A Bespoke Custom Suit is on a whole different level. The process begins similar to MTM considering measurements, fabric selection and other personalization options, however the main distinction between these 2 types of custom suits is the pattern type.
Bespoke custom suits are made by creating a pattern from scratch vs. a standardized pattern.
Also an additional fitting is required with bespoke suits, which is a basted try- on. If you've ever seen a suit jacket that looks unfinished with visible threading, those are the temporary basting threads.
During this phase any fit adjustments are made prior to finalizing the garment.