for sale的意思是「待售」「供出售」，即「用於出售」。on sale有兩個意思，一是表示「出售」，與for sale不同，它表示的是「進入銷售環節」「處於被銷售的狀態」；二是表示「廉價出售」「打折出售」。
sale
noun
[mass noun]the exchange of a commodity for money; the action of selling something
賣，出售
we withdrew it from sale.
我們把它撤下不賣了。
the sale has fallen through.
這樁買賣已經告吹。
(sales)a quantity or amount sold.
銷售量，銷售額
price cuts failed to boost sales.
減價沒能增加銷量。
(sales)the activity or business of selling products.
銷售活動，銷售
director of sales and marketing.
銷售部主管。
an event for the rapid disposal of goods at reduced prices for a period, especially at the end of a season
（尤指季末的）廉價出售，賤賣
a closing-down sale.
歇業大甩賣。
[often with modifier]a public or charitable event at which goods are sold.
義賣
a public auction.
拍賣
習慣用語
(up) for sale
offered for purchase; to be bought
供出售；待售
cars for sale at reasonable prices.
價位合理的待售小轎車。
on sale
offered for purchase
供出售；上市
the November issue is on sale now.
11月號的雜誌現在已經在發售了。
(N. Amer.)offered for purchase at a reduced price.
(北美)削價出售
sale or return
[usu. as modifier](Brit.)an arrangement by which a purchaser takes a quantity of goods with the right of returning surplus goods without payment
(英)剩貨包退，可退貨經售
booksellers normally order books on a sale-or-return basis.
書商通常根據剩貨包退的原則定購圖書。