What's the difference between caulk and sealant?

The main thing is flexibility and what happens after it sets. Sealants stay rubbery and stretchy once they cure, so they can handle movement without cracking. Caulk hardens into something solid and paintable, but if the surface shifts even a little - which happens everywhere from temperature changes or settling - it'll split open on you. I learned this the hard way when i used regular caulk around my kitchen sink. After one winter the cracks came back, and I had to redo it.

Where you use each one matters. Caulk works great for filling gaps in drywall, trim, or places that basically don't move. It's cheaper, easier to paint over, and looks cleaner for trim work. Sealant is what you want around tubs, showers, windows, and anywhere there's any flex or moisture. Silicone and polyurethane sealants are the heavy hitters - they'll last way longer and actually seal against water instead of just filling a gap. Even if a sealant looks a bit rougher or doesn't take paint as nicely, it's worth it in wet areas or joints that move.

The confusion comes because people use the words interchangeably, but in practice they're doing different jobs. Pick the wrong one and you're dealing with it again in a year or two. Grab sealant for anything that breathes or gets wet, caulk for everything else.