Automated Customer Account Transfer Service - ACATS

What Does Automated Customer Account Transfer Service - ACATS Mean?
A system that facilitates the transfer of securities from one trading account to another at a different brokerage firm or bank. The National Securities Clearing Corporation (NSCC) developed the ACATS system, replacing the previous manual asset transfer system with a fully automated and standardized one.

Investopedia explains Automated Customer Account Transfer Service - ACATS
Stocks, bonds, cash, unit trusts, mutual funds, options and other investment products can be transferred via the ACATS system. Only NSCC-eligible members and Depository Trust Company member banks can use the ACATS system. This is the system in which processes Automated Customer Account Transfers (ACAT).