lockunspent unlock [{"txid":"txid","vout":n},...]

Updates list of temporarily unspendable outputs.
Temporarily lock (lock=true) or unlock (lock=false) specified transaction outputs.
A locked transaction output will not be chosen by automatic coin selection, when spending bitcoins.
Locks are stored in memory only. Nodes start with zero locked outputs, and the locked output list
is always cleared (by virtue of process exit) when a node stops or fails.
Also see the listunspent call

1. unlock (boolean, required) Whether to unlock (true) or lock (false) the specified transactions
2. "transactions" (string, required) A json array of objects. Each object the txid (string) vout (numeric)
[ (json array of json objects)
"txid":"id", (string) The transaction id
"vout": n (numeric) The output number

true|false (boolean) Whether the command was successful or not


List the unspent transactions
> bitcoin-cli listunspent

Lock an unspent transaction
> bitcoin-cli lockunspent false "[{\\"txid\\":\\"a08e6907dbbd3d809776dbfc5d82e371b764ed838b5655e72f463568df1aadf0\\",\\"vout\\":1}]"

List the locked transactions
> bitcoin-cli listlockunspent

Unlock the transaction again
> bitcoin-cli lockunspent true "[{\\"txid\\":\\"a08e6907dbbd3d809776dbfc5d82e371b764ed838b5655e72f463568df1aadf0\\",\\"vout\\":1}]"

As a json rpc call
> curl --user myusername --data-binary '{"jsonrpc": "1.0", "id":"curltest", "method": "lockunspent", "params": [false, "[{\\"txid\\":\\"a08e6907dbbd3d809776dbfc5d82e371b764ed838b5655e72f463568df1aadf0\\",\\"vout\\":1}]"] }' -H 'content-type: text/plain;'
Don't trust. Verify. Docs extracted from src/rpcwallet.cpp#L1743-L1779.