Traces provide information about the route a request follows through your code. This shows what parts of the program is used and is often accompanied with logs or parameters.
More concretely they can help you glean information of the following things:
- Execution path & sequence of code paths in a request
- Performance of the code when the timings are captured
- Parameters and dependencies of the code when these are captured
When not careful, traces can slow down a program.
In short you could say that traces are sequences of logs.