GC_CONCURRENT
Means that Garbage Collection happens in a parallel manner. Without affecting any performance.
freed 440K
This particular cycle of GC has freed 440k memory.
free 3317K/6471K
Available and total Heap Memory Details.
external 0K/512K
External Memory available for your app(other than heap).
4ms+7ms
4ms at the beginning of GC was paused and at the end 7ms was consumed by GC.
That is, during this GC, all your activities were suspended for a total of 11ms , 4ms at the beginning and 7ms at the end.
For more info on this, please watch this video. He explains this very clearly.
Patrick Dubroy Memory Management