The movement of matter across a cell membrane against a concentration difference is called

Active transport.

Explanation:

The molecules can pass through the cell membrane by the process of transport according to the concentration gradient. Two main types of transport are active transport and passive transport.

Active transport requires energy in the form of ATP. The active transport moves the molecule towards the higher concentration from the region of lower concentration. The molecules move against the concentration gradient in the active transport.

Thus, the answer is active transport.

The movement of matter across a cell membrane against a concentration difference is called an Active Transport.