It means old. Maybe those things considered classic were once good, enough to still be around, but nothing remains good forever.
Classical music for example, sure its calming, yet some more modern music is calming too. It has no words, usually. Yes it can provide feeling, but not as much as more modern things with music with feeling and lyrics that speak too you. Its been outgrown, it once was good, but now has been replaced.
Classic literature has long outgrown its relevance. We can learn just as much from modern literature. Sure, The Adventures of Huckleberry Finn is a good story (if you can understand what they're saying), but its no longer relevant to modern life. The themes are relevant, but not as they are presented. More importantly, we can get the same lesson from other books that don't have the "classic" label. Tolkien might have first outlined the more modern form of fantasy literature, but the world is beyond him now. Read Patrick Rothfuss instead.
What we need to focus on is that the world is constantly changing. Those that have replaced the classics have learned what they can from them. All we must do is learn from modern works, and we'll learn more than classics could ever teach us. The idea that modern walks are flawed is wrong. We don't have to wait 50 + years for what is modern today to be considered classic so we can learn from it. By then, we'll have more modern things to focus on. Modern work learns from slightly less modern works, which learned from pre-modern works, which maybe learned from post-classic works. There is no reason to go all the way back. Learn from today's works, and you'll learn everything important from past works already edited and presented, ready to be smoothed down one more time from a new modern mind.