Modular origami is those models assembled from multiple pre-folded pieces. Generally all or most or these pieces are the same, and fit together to form a geometric shape. This category also lists sites which connect origami to math, usually geometry.
Sites submitted should be those which fall into one of two areas.

First is those linking origami to math topics, usually geometry. This can take various forms, such as methods of creation, theories, and resulting models.

Modular sites should be those focusing on models made from similar pre-folded pieces. Generally they fit together without glue or tape, but there can be some exceptions.

If a site is a general origami site with just an article on math, or a couple of modular diagrams, they should be submitted to the main origami category instead.