what is log and when we use log and why we use log?

Hello every one

I have some questions about log in java?

what is log?
when we use log?
why we use log?

Thank you in advance

Log, it's log, it's big, it's heavy, it's wood...

A log is just a recording of what the program is doing. You can create a log by just printing to a file, or there are frameworks for more detailed logging. What has google told you?

It's better than bad, it's good!