The typical distinction is that altruism is a subset of kindness where the action is either selfless or sacrificial. You can show kindness with an intent to benefit from it, while altruism requires that you have no substantial intent to gain.
If you take the word at face value, altruism is generally a useful term. More often, discussions of altruism veer toward discovering the hidden, self-serving motives in it. Such motives include anything from kin selection in evolution to the warm feelings Gandhi might've gotten from his acts of service.
On the biology side, see The Selfish Gene for more. On the philosophical side, free will is one place to start.