The columns are as follows:
Timer Id: This gives the name of the block of code being executed
Time: The time it took to complete in seconds
Avg: The average time it took to complete in seconds
Cnt: Short for Count. This represents the number of times this individual block ran to generate the output required
Emalloc: The amount of memory PHP ( the programming language on which Magento runs) assigned to this single operation. This is again represented in bytes.
RealMem: The actual amount of memory used to perform the operation.