On sale
Definition 1 of 2
Pro Tip 1/3Limited Time
Often implies a limited time offer to encourage immediate purchase. 
This special on-sale offer ends Sunday.
Pro Tip 2/3Seasonal Sales
Sales are common during season ends, like 'end-of-summer sale'. 
Many jackets go on sale in the spring.
Pro Tip 3/3Clearance Items
'On sale' can mean clearing stock, potentially less popular items. 
The old model TVs are on sale to clear space.