What is the difference in meaning between "pattern" and "rhythm"?

The words have different but related meanings. A pattern is a general term for anything that has repetition or other regularity, so it can be seen, heard or otherwise perceived. People often talk about patterns on a dress, or patterns in behavior.

A rhythm is a pattern in time, most commonly used to describe music or speech. Another common use of rhythm is when one is said to be "in a rhythm." This means a person is doing something at a sustainable and comfortable pace, almost as if they were following the beat of music.

To me, a rhythm happens in time, whereas a pattern may happen over any dimension, usually space. In other words, a rhythm is a temporal pattern. :-)

But of course, we often employ these words metaphorically, so these nuances are lost.