Made-to-measure clothes, curtains, and similar things are made to fit your size, not a standard shop size. Someone measures you (or your window), then cuts and sews to those numbers. It sits between ready-made (you pick it off a rail) and fully one-of-a-kind design: the style may be a known pattern, but the fit is yours. In British English this phrase is very common for suits and curtains; American English often says custom-made or tailored instead, though made-to-measure is still understood. Shops use it as a selling point: you pay more, and you wait, because the thing does not exist until they have your measurements. People sometimes stretch it to anything “fitted to you,” even software, but the home of the phrase is cloth and soft furnishings.