What is the difference between trim, bleed, and safe area?

Three print terms the Cover Maker handles for you, but worth understanding:

• Trim — the final size of the printed book after it's cut (e.g. 6 × 9 in). It's the size the reader holds.
• Bleed — a small margin of artwork (usually 0.125 in) that extends past the trim line on every edge. Printers can't cut perfectly to the millimeter, so your background art runs into the bleed and gets trimmed off, guaranteeing color reaches the very edge with no white slivers.
• Safe area — an inner margin, inside the trim, where you keep anything important (title, author name, spine text). Because the cut wanders slightly, text too close to the edge risks being shaved. Keep text inside the safe area.

The Cover Maker builds your export with the correct bleed already added and shows guides for the trim and safe zones, so you can position text with confidence. Text that strays outside the safe area is the usual cause of a KDP "outside the safe area" warning.