In auctions generally, a lot is one thing being sold as one unit — whether that is a single object or thirty objects sold together. A saleroom numbers its lots and works through them in order.
Metzee does not use the word. It says item. So if you have arrived here from an auction background looking for the lot number, there is nothing to find: an item has a title, not a number.
What the word is actually useful for
The second sense — several objects sold as one unit. That is a real thing on Metzee and it has its own name: a bundle.
A bundle is one listing holding several objects, with one price and one winner. Six paperbacks, a set of tools, a job lot of fabric. It is one item in the app's sense even though it is many things in your hands. How to list a bundle
Why the distinction matters when you buy
Because what you are bidding on is whatever the listing says it is, and the two mistakes are opposite:
Assuming one when it is many. The photograph shows a shelf of books; the listing is for one of them.
Assuming many when it is one. The photograph shows the whole set; the description says "one bowl, the others are for scale".
Both are read-the-description problems, and both are commoner on bundles than on anything else. Ask in the chat if it is not plain — a seller would far rather answer than take a return. How a live auction show works
For sellers
If you are used to saying "lot", say bundle or just list what is in it. The word a buyer searches for is the thing itself — "six Wodehouse paperbacks" finds buyers; "Lot 14" finds nobody.
And say what is not included, because that is where bundle returns come from. How to write a good description
The other auction words that do carry over
Some of the vocabulary is the same here as in any saleroom: reserve, increment, under-bidder. Those are real on Metzee and each has its own page.
More: every Metzee term, explained, auction words, explained, how to list a bundle.