The confusion seems to be arising because in the UK the levels are named "lecturer, senior lecturer, reader, professor" and in the US the levels are named "assi

The confusion seems to be arising because in the UK the levels are named "lecturer, senior lecturer, reader, professor" and in the US the levels are named "assistant professor, associate professor, (full) professor". In the UK "professor" is a very high ranking position that most academics don't attain. In the US "professor" just means that you teach, basically.