What does a memory leak look like in Instruments

Could an experienced Instruments user tell me what a memory leak looks like in Instruments? When I profile my application I get occasional orange spikes in the leaks instrument, i.e a sharp spike that returns to the baseline, is this a memory leak?

I searched for screenshots online to try and clarify and the only example I could find showed a persistent blue block in the leaks instrument, similar to a standard trace you might expect in the object allocations instrument. ( http://www.cimgf.com/2008/04/02/cocoa-tutorial-fixing-memory-leaks-with-instrume nts/). This makes me think that perhaps the orange spikes I see aren't leaks?

Can anyone clarify what a leak looks like in instruments?

Thanks