A simile compares two unlike things using like or as (for example, “cheeks like roses”). A metaphor applies a word or phrase from one thing to another to suggest likeness without those linking words (for example, “the baby’s cheeks were newly bloomed roses”).
Both are figures of speech that create a comparison, but a metaphor is more direct—it treats one thing as if it is another—while a simile keeps the comparison explicit. Writers choose between them for tone: metaphors often feel stronger; similes can feel lighter or more precise.