What are the "bytes touched" in V8 Parse processor?

The number of bytes seen/processed by the parser or preparser. (I don't know why it would ever be negative, that seems surprising; but maybe there's a good reason for it.)

What happens in the pre-parse time?

Preparsing is the initial quick pass over code that will be lazy-compiled later. It's required in order to:

• find out which functions exist, and where in the source they are
• find out which variables from their outer scopes they refer to, so that these variables can be context-allocated
• throw "early errors" as required by the JS spec
• and maybe a few other things that I'm not thinking of right now.

For functions that will be eagerly compiled immediately, preparsing can be skipped. Usually it's beneficial to preparse and lazy-compile though (so any future readers of this: please don't feel tempted to minimize preparsing time, that'd most likely be counter-productive!).

what are the these terminologies such as baseline time, resolution time and nesting level mean?

"baseline time": time for baseline (non-optimized) compilation
"resolution time": time for variable resolution
"nesting level": when a function is defined inside another function, they're "nested". Obviously this can go many levels deep.

Even though I executed the function, it still shows up as "non-executed" in parse time. Why is it so?

Because tracking executed functions in the Parse Profiler is currently not implemented, apparently because nobody needed it.