i define racism as bigotry/discrimination/hatred based on race. power (whatever that really is) is a completely separate issue, though obviously they can play together quite well.
institutional racism is very real. but claiming that is the only context in which actual racism exists seems like both an abstraction and a cop-out to me. it removes responsibility and agency from individuals, when individuals are in fact the only concrete actors that can demonstrate racism. even a massive, racist institution like the u.s. legal system consists of nothing more than a shitload of individuals, who - whether or not they are following official policy (which was of course defined and codified by individuals) - may or may not act in ways that can be described as racist. placing racism solely in the realm of institutions kind of legitimizes the old "i'm just doing my job" excuse that supposedly got played out in nazi germany.
as to "reverse racism" (a term that makes absolutely no sense to me): my black (ex)wife of over 20 years frequently saw, and commented on, the racism she observed in other black folks as a result of our happy mixed-racedness. the idea that blacks cannot be racist against whites is absurd to me, and to the many dozens of black people in my extended family. when sista souljah came out with that "blacks cannot be racist" statement during the rodney king shit, my wife and i both nearly busted a gut.
ever see the spike lee movie "school daze"?
[i suspect this will not be a very popular answer]