Originally Posted by njkayaker

Historically, road bikes used narrow tires with high pressure. That set-up works for smooth roads but is less comfortable and slower on rough roads. More recently, road bikes are being fitted with wider tires (28mm instead of 25 or 24). So a new road bike will be OK for rougher pavement. That is, it's the width of tires that you should be considering. (Gravel bikes let you use much wider tires than road bikes.)

There isn't a hard line between road bikes and gravel bikes. You might be able to find something that sits in between a "true" road bike and a "true" gravel bike.

"Gravel" wasn't a good term to apply to gravel bikes. There are quite a lot of unpaved and gravel roads that don't need a "gravel" bike (that a road bike can handle fine).