A pledge of shares means a shareholder provides their shares as security for a debt, such as a loan. If the debt is not repaid, the pledgee may have the right to take the shares.
A pledge must be noted in the share ledger so it is clear that the shares are pledged and to whom. This matters for traceability and to protect both lender and owner. It also affects what applies in a future transfer of shares.

Locking of a block of shares means a pledged block of shares is blocked so it cannot be transferred.
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A notice of pledge (denuntiation) is a notice that gives the pledgee protection against third parties.
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A share ledger is a record of a company's shares and who its shareholders are.
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