A spec sheet (specification sheet) is the document that defines a garment in measurable terms: where it is measured, the target size for each point, and how much variation is acceptable. A garment spec sheet gives a supplier one clear reference to build and check each style against.
The core of a spec sheet is the measurements. Each point of measure (PoM) has a code, a name, a measure type and clear start and stop locations, with a target value for every size in the range. Grade rules set how those values change from one size to the next, and a tolerance (+/-) shows how far a measurement may vary. A measurement description, a technical drawing and a How to Measure manual explain how to read the numbers, so the same garment is measured the same way everywhere.
The two terms are often used side by side. A tech pack is the full build document, with the bill of materials, artwork, trims and construction details. The spec sheet is the measurement part of it: the size specification that a fashion garment specification sheet is judged against. Give suppliers only the specs they need, and leave room for them to adjust fit, weight and pattern where it makes sense.
In Delogue, the Size Chart is where measurements and grading are built and reviewed, and How to Measure files can be attached next to them. The team and its suppliers then work from the same specification instead of separate copies. See how to spec a garment with points of measure.