Most men in their sartorial journey start out with off-the-rack clothing known as ready-to-wear (RTW). The lion's share of the $50 billion US menswear industry goes to RTW sales of suits, jackets, trousers, dress and sports shirts, etc.
RTW apparel are characterized by the fixed nature of their construction and features. RTW suits for example are mass, machine produced in factories, typically with "fused" interlinings in the lapel and coat front. Garment sizes are made for the "average" person. The advantage of RTW suits is affordability as very little human tailoring is involved. The downside is that fused suits often feel stiff and may not last as long as fully canvassed ones.
MTM or made-to-measure is one step up in terms of construction (usually canvassed or half-canvassed) and feature selection. The customer typically selects a fabric (often from a selection numbering in the hundreds), is measured by a specialist sales associate or tailor and selects certain features (such as slanted jacket pockets and lapel width). MTM is often used by a retailer to provide "custom" tailoring. The measurements are used to alter a stock pattern (e.g. a 40R) and the garment is actually made by a "cut-make-trim" factory such as Martin Greenfield Clothiers in Brooklyn, New York, Adrian Jules in Rochester, New York or John H. Daniel in Knoxville, Tennessee.
Bespoke tailoring offers the most customized experience and indeed some aficionados believe it is the sine qua non of a gentleman's sartorial existence. The heart of bespoke tailoring lies in fully individualized pattern making and cutting. Even so, sewing and construction of specific parts of a garment may be outsourced to a specialist tailor (e.g. buttonhole sewing). For certain hard-to-fit individuals, bespoke may be the only satisfactory solution. For certain individuals who are highly exacting in their requirements, bespoke may also be the only satisfactory way to dress.