What does [login] mean?

Hi I’m just curious what does [login] under username mean? I’ve been regularly checking my user’s history and I’ve noticed an anomaly. All of the user’s attempts are showing failed but the user’s username is only showing [login] instead of the username and that user shows a different IP address per login. What does this mean? I really want to know because this user is might looking for ways to hack my site. Thank you