A lasque is a flat, plate-like cut of diamond traditionally produced in the Indian sub-continent, characterised by a very large, broad table on top, a shallow pavilion below, and an irregular outline that follows the natural shape of the rough rather than imposing a symmetrical geometry on it. The cut is a survivor of pre-modern Indian lapidary, where the priority was to retain weight and to produce a window-like stone suitable for kundan setting, rather than to maximise return of light through the table.

Mechanically a lasque is closer to a polished slice than to a brilliant. The pavilion may carry only a handful of small facets, sometimes none at all beyond a polished surface; the crown is dominated by the table; the girdle outline is whatever the rough allowed; and the stone is normally just a few millimetres deep regardless of carat weight. The result is a thin, light-coloured plate with limited fire or dispersion, but with an unusual presence: the broad face of the stone shows colour and inclusion patterns directly, and large lasques have been used for centuries in Mughal-style jewellery to act as windows over enamelled or foiled backings.

In the modern trade lasques are encountered chiefly in two contexts. They form the structural diamonds of antique kundan and polki jewellery, where the foil-backed setting compensates for the cut's lack of inherent brilliance. They also appear, occasionally, as architectural feature stones in contemporary high-jewellery design, where a designer wants the geometry of a flat diamond rather than the optical performance of a brilliant. They are graded by GIA on the regular D-to-Z, IF-to-I3 scale, but cut grading is not normally applied because the cut is by definition not a standard one.