What is the difference between a whatnot and an étagère?

In practice, nothing. The listings use both words for the same free-standing stand of open tiers, and étagère is simply the French term. The spelling is unusually unsettled for this form. Whatnot, what not, wot-not, wotnot, watnot, ettagere and etagere all appear in titles for what is essentially one object.

Which wood is most common?

Mahogany, by a clear margin. Oak follows, then walnut, rosewood and pine. Beyond those, unusual timbers surface now and then. Padouk, amboyna, birdseye maple, burr elm, satin birch, limewood, yew, cherry and olive wood each appear once or twice, along with a Ceylonese ebony and satinwood étagère.

How old are most of these?

The dated field spans 1750 to 1930. Victorian and 19th-century entries lead, with Regency, Georgian and Edwardian behind them. Precision is the exception. Only 289 of 853 listings give a clean year, and one carved oak wall shelf is entered as 17th century.

Are kitchen plate racks part of this category?

Yes, and they make up roughly one in ten. Plate racks, delft and delph racks, dresser racks and spice racks all sit under the heading, usually in oak or pine. French baker's racks belong here too - boulangerie and patisserie racks turn up, and one stands at the very top of the range.

How often do pairs come up?

Not often: 42 titles in 853. Pairs of Regency rosewood display shelves, George IV yew wood shelves and matched corner whatnots are the sort of thing that appears. Dealers hedge the wording, which tells you something. "Near pair" and "matched pair" are both used.

Do many carry a maker's name?

Very few. Gillows is the only name carried by more than a couple of dealers across the whole category. Even then it is usually qualified rather than stated, appearing as "possibly Gillows" or "attributed to Gillows". About a hundred sets come to market on Sellingantiques in a year, listed by 217 different dealers, and the great majority are described by timber, period and form alone.