A more thorough explanation:

Immobilize, verb. To make something unable to move or be moved; especially, to turn movable property into immovable property or to turn circulating capital into fixed capital.

• The police officer used handcuffs to immobilize the suspect.
• The doctor immobilized the patient's broken arm with a cast.
• The company decided to immobilize some of its assets by investing in real estate.

The first two examples illustrate the literal meaning of immobilize, which is to physically prevent something from moving. The third example shows how the term can also be used in a financial context, where assets are turned into fixed capital, meaning they cannot be easily sold or converted back into cash.