What does this mean?

[celeron]

Hi I have a jailbroken iPod touch 4.

So yesterday I was playing angry birds and when I hit the home button it said that springboard crashed and I was in safe mode.

Then I hit reload or something like that and went back to normal.

So question is why does this happen and how I can Prevent it from happening? Is this bad?

[Simon]

Something from cydia probably caused it. That safe mode is there to protect the phone.