In the US, the term "straight in" in a approach clearance was a way to ensure the crew, joined the final course and did not fly a course reversal. It is described this way in the FAA AIM and is really a holdover from the early radar days.
I don't think there is any reference to it in PANS-OPS or Doc 4444. I wouldn't consider it a clearance for a visual approach, though
GF