A Handler is something that transforms log events to concrete outputs (files, disks, writes to stderr, etc.) via side effects.
A Logger is what programs use to produce, transform, etc. log events.
Both are abstract interfaces with arbitrarily many possible implementations. Both are defined in terms of their user-facing capabilities. I'm not sure how those definitions would differ. Both accept log events and do something with them. That interface is the same.
A Handler is something that transforms log events to concrete outputs (files, disks, writes to stderr, etc.) via side effects.
A Logger is what programs use to produce, transform, etc. log events.
Both are abstract interfaces with arbitrarily many possible implementations. Both are defined in terms of their user-facing capabilities. I'm not sure how those definitions would differ. Both accept log events and do something with them. That interface is the same.