What is a standard or conventional name for a column representing display order? For example, a junction table associating a product and its pictures:

create table product_picture (
  product_id bigint not null references product(id),
  picture_id bigint not null references picture(id),
  some_column int not null
);


What is a common/conventional, short, general, name for some_column if it represents the display order of the photos?

order, sort, and sequence are out, as they are keywords.
It depends on what your philosophy is around column naming.  

If you go for very descriptive long column names, then display_order is perfectly fine, since that is exactly what your column contains.  

If you are comfortable with shorter names that may seem a little cryptic, but which can be figured out pretty easily, then you could use seq or ord.  For English speakers, seq is pretty unambiguous as there aren't a lot of words that this could reasonably represent.  I would pick that over ord for that reason.