OP_CAT is an opcode, which stands for
operation code, that was part of the original
Bitcoin scripting system. It was used to
concatenate, or join, two data sets or
elements from a stack, and then put them back
into the stack.
ABOUT US
This allowed for creating complex covenants,
which are rules or conditions for how bitcoins
can be spent. OP_CAT was disabled by Satoshi
Nakamoto in 2010, due to security concerns,
such as the possibility of creating DoS
(Denial of Service) attacks by using OP_CAT
and OP_DUP together to create extremely large
stack elements.
Some developers have proposed to re-enable it
with a soft fork, which is a
backward-compatible change to the Bitcoin
protocol. Re-enabling OP_CAT could enable more
functionality, scalability, and security for
Bitcoin transactions, but it could also
introduce new risks and complexities.