why --user used constantly in curl examples?

[Bitcoin]

why --user used constantly in curl examples?

curl --user myusername --data-binary '{"jsonrpc": "1.0", "id":"curltest", "method": "encryptwallet", "params": ["my pass phrase"] }' -H 'content-type: text/plain;' http://127.0.0.1:8332/

https://bitcoincore.org/en/doc/0.16.0/rpc/wallet/encryptwallet/

what's it?

looks  like username:password but why then it's called 'myusername'

Source: why --user used constantly in curl examples?