Alumbrados are a group of people who lived in Spain a long, long time ago. They believed that they could get closer to God by thinking really hard about Him all the time. This idea is called "contemplation." They believed that if they did this, they could understand God better and become better people.
Now, these people also thought that they didn't need church leaders to help them get closer to God. They thought that they could just do it on their own. This was different from what the church leaders at the time were teaching.
Some church leaders did not like this, so they said that these alumbrados were spreading bad ideas. They said that they were heretics, which means they did not believe in the right things. The church leaders started to investigate them and some of them were put in jail.
So, in a nutshell, alumbrados were people who believed they could get closer to God through contemplation and did not believe they needed church leaders to do so. Their ideas were considered heretical by the church at the time.