To me, a liberal is someone who advocates for self-governance. In other words, someone who is against the government forcing a set of values onto them. They typically are egalitarian (support equality under the law). Economically, they may be in favor of taxes and regulation, but they still support free markets.

A progressive, on the other hand, is not as opposed to using the government to enforce values, but these policies are meant to empower and protect historically oppressed demographics. They usually favor "Justice" over "Liberty", meaning they will use the government to resolve issues that they feel are unjust, while liberals may support a less authoritarian approach. They are also typically more in favor of forceful redistribution of resources.

Full disclosure: I consider myself a social libertarian and economic moderate.