mark down

to reduce the price of something, usually in order to encourage people to buy it:
Low consumer demand has forced us to mark down a wide range of goods, sometimes by as much as 30 percent.
Shares in the electricity companies were marked down following the announcement of the new energy tax.

to write something on a piece of paper in order to make a record of it:
I've marked down the number of each item sold.
Look carefully at these questions and mark your answers down in the right-hand column.
(Cambridge Advanced Learner's Dictionary & Thesaurus からの mark sth down の定義 © Cambridge University Press)

ビジネス英語
to reduce the price of something, usually in order to encourage people to buy it:
mark sth down by sth Low consumer demand has forced us to mark down a wide range of goods.
Everything in the store is marked down today.

to make the value of something lower:
Shares in the electricity companies were marked down following the announcement of the new energy tax.
They have marked down their forecasts for growth.
(Cambridge ビジネス英語辞典 からの mark sth down の定義 © Cambridge University Press)

- Cambridge Dictionary