Methods that do not use mathematical or statistical research are sometimes seen as being soft or inferior, i.e. not being that powerful or reliable or even valid.
Спасибо!

Soft Ideals and Arithmetic Mean Ideals
This article investigates the soft-interior (se) and the soft-cover (sc)
of operator ideals. These operations, and especially the first one, have been
widely used before, but making their role explicit and analyzing their interplay with the arithmetic mean operations is essential for the study in [10] of the multiplicity of traces. Many classical ideals are “soft” i.e., coincide with their soft interior or with their soft cover, and many ideal constructions yield soft ideals

Yippie, это не про то, вы залезли в глубокую математику.
Тут soft как бы антоним к solid.