1 general:: Phrase(s): on sale available for sale at a reduced price. (Always implies lower than usual sale price.) • These pots are on sale for $20. • I bought these pants on sale for half price.
McGrawhill's American Idioms And Phrasal Verbs
2 general:: At a reduced price, as in These rugs have been on sale for a month. The use of sale for disposing of goods at lowered prices dates from about 1860.
American Heritage Idioms