Kibana Status page - what does it show?

On Kibana status page it shows Heap Used (GB). It is Kibana Heap or Elastic Search heap? Also it is growing, but we only query the data for the last day, does elasticsearch keep all indices in memory that is why it growing?

Kibana heap.

ES doesn't keep indices in memory no. I am not sure why the KB heap use would increase though sorry.

Thanks, I noticed it gtown until 2gb and after that dropped to 100mb apprx. Why Kibana can consume so much heap? Is it dropped.because of GC and why it was triggered so late? How to set a limit for a heap?